INTERMOUNTAIN ALFALFA MANAGEMENT

I N T E R M O U N T A I N A L F A L F A M A N A G E M E N T

I N T E R M O U N T A I N A L F A L F A

M A N A G E M E N T

Technical Editors

Steve B. Orloff, EditorHarry L. Carlson, Co-Editor

Associate Editor

Larry R. Teuber

P U B L I C AT I O N 3 3 6 6

University of CaliforniaDivision of Agriculture and Natural Resources

G E N E R A L WA R N I N G O N T H E U S E O F C H E M I C A L S

Pesticides are poisonous. Always read and carefully follow allprecautions and safety recommendations given on the con-tainer label. Store all chemicals in their original labeled con-tainers in a locked cabinet or shed, away from foods or feeds,and out of the reach of children, unauthorized persons, pets,and livestock.

Confine chemicals to the property being treated. Avoiddrift onto neighboring properties, especially gardens contain-ing fruits and/or vegetables ready to be picked.

Mix and apply only the amount of pesticide you will needto complete the application. Spray all the material accordingto label directions. Do not dispose of unused material by pour-ing down the drain or the toilet. Do not pour on ground: soilor underground water supplies may be contaminated. Followlabel directions for disposing of container. Never burn pesti-cide containers.

Phytotoxicity: Certain chemicals may cause plant injury ifused at the wrong stage of plant development or when temper-atures are too high. Injury may also result from excessiveamounts or the wrong formulation or from mixing incompati-ble materials. Inert ingredients, such as wetters, spreaders,emulsifiers, diluents, and solvents, can cause plant injury.Since formulations are often changed by manufacturers, it ispossible that plant injury may occur, even though no injurywas noted in previous seasons.

To simplify information, trade names of products have beenused. No endorsement of named products is intended, nor iscriticism implied of similar products that are not mentioned.

The University of California, in accordance with applicable Federal and State law and Universitypolicy, does not discriminate on the basis of race, religion, color, national origin, religion, sex, disability,age, medical condition (cancer-related), ancestry, marital status, citizenship, sexual orientation, or statusas a Vietnam-era veteran or special disabled veteran. The University also prohibits sexual harassment.

Inquiries regarding this policy may be addressed to the Affirmative Action Director, University ofCalifornia, Agriculture and Natural Resources, 300 Lakeside Drive, 6th Floor, Oakland, CA 94612-3560. (510) 987-0096.

2m-rev-6/97-WJC/TM/NS

For information about ordering this publication, contact

University of CaliforniaDivision of Agriculture and Natural ResourcesCommunication Services—Publications6701 San Pablo AvenueOakland, California 94608-1239

Telephone (800) 994-8849 or (510) 642-2431Fax (510) 643-5470 e-mail inquiries to [email protected]

http://danrcs.ucdavis.edu/

Publication 3366

ISBN 1-879906-24-4

Library of Congress Catalog Card No. 94-61790

© 1997 by The Regents of the University of California, Division of Agriculture and Natural Resources.

Line drawings of damsel bug, green lacewing, alfalfa caterpil-lar, armyworm, blister beetle, grasshoppers, and thrips werereprinted with the permission of Simon & Schuster from theMacmillan College text Entomology and Pest Management byLarry P. Pedigo. Copyright ©1989 by Macmillan PublishingCompany, Inc.

All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means,electronic, mechanical, photocopying, recording, or otherwise,without the written permission of the publisher and the authors.

Printed in the United States of America.

On the front cover: Pictured is the second cutting of a center-pivot-irrigated alfalfa field at the Prather Ranch in Butte Valley,California. Majestic Mount Shasta appears in the background. Thephotograph was taken in July 1993.

On the back cover: At the Prather Ranch alfalfa shows its adaptabil-ity to a wide range of soil and climatic conditions and serves forboth off-farm sales and on-farm use.

PHOTOS BY STEVE ORLOFF

A C K N OW L E D G M E N T S

This book is a product of a collaborative effort by theauthors, under the auspices of the University ofCalifornia Intermountain and Alfalfa workgroups.Encouragement and initial funding were provided byDivision of Agriculture and Natural Resources—North Region, Terrell P. Salmon, Director.

Technical EditorsSteve B. Orloff, Editor

Farm Advisor, Siskiyou CountyHarry L. Carlson, Co-Editor

Director, Research and Extension Centers and FarmAdvisor, UC Davis

Associate EditorLarry R. Teuber

Professor of Agronomy and Range Science, UC Davis

Contributing AuthorsRoger W. Benton

Retired Farm Advisor, Siskiyou CountyHarry L. Carlson

Director, Research and Extension Centers and FarmAdvisor, UC Davis

R. Michael Davis Extension Pathologist, Department of Plant Pathology,UC Davis

Rhonda R. Gildersleeve Farm Advisor, Inyo-Mono counties

W. Paul Gorenzel Extension Staff Research Associate, Department ofWildlife, Fish, and Conservation Biology, UC Davis

Blaine R. Hanson Extension Irrigation and Drainage Specialist,Department of Land, Air, and Water Resources, UC Davis

Donald L. Lancaster County Director/Farm Advisor, Modoc County

Vern L. Marble Extension Agronomist Emeritus, Department ofAgronomy, UC Davis

Daniel B. Marcum Farm Advisor, Shasta-Lassen counties

Kristen D. Marshall Postgraduate Researcher, Department of PlantPathology, UC Davis

Roland D. Meyer Extension Soils Specialist, Department of Land, Air,and Water Resources, UC Davis

Steve B. Orloff Farm Advisor, Siskiyou County

Daniel H. Putnam Extension Forage Agronomist, Department ofAgronomy, UC Davis

Terrell P. Salmon Wildlife Specialist, Department of Wildlife, Fish, andConservation Biology, UC Davis, and Director,Division of Agriculture and Natural Resources—North Region, UC Davis

Jerry L. Schmierer Farm Advisor, Lassen County

Becky B. Westerdahl Extension Nematologist, Department of Nematology,UC Davis

Principal ReviewersCarol A. Frate

Farm Advisor, Tulare CountyShannon C. Mueller

Farm Advisor, Fresno CountyDaniel H. Putnam

Extension Forage Agronomist, Department ofAgronomy, UC Davis

v

Special Thanks

The following persons generously provided informa-tion, offered suggestions, reviewed draft manuscripts,helped obtain photographs, or otherwise helped inmanuscript preparation:

Donald L. Bath, W. Michael Canevari, David W. Cudney, Randy L. Dovel, Daniel J. Drake, Bill Ferlatte, Bill B. Fischer,Larry D. Godfrey, David B. Hannaway, Lawrence W. Mitich, Donald A. Phillips, Terry L. Prichard, C. Alan Rotz, Michael W.Stimmann, and Helga K. Struckman.

SponsorsThe production costs of this publication were offset bygenerous contributions from the following companiesand organizations:

Allied Seed Cooperative, Inc.American CyanamidAmerica’s AlfalfaBaker Performance Chemicals Incorporated

Magna Herbicides BASFBasin Fertilizer & Chemical Co., Inc.California Crop Improvement AssociationDEKALB Genetics CorporationDowElancoDunham & Livesay, Inc.DuPont Agricultural ProductsFMC Corporation, Agricultural Chemical GroupGermain's, Inc.High Mountain Hay Growers Co-op

Highland Seed & SupplyI.K. Seed Research Inc.Intermountain Hay GrowersMacdoel Fuel & ScalesMacy’s Flying Service, Inc.McArthur Farm Supply, Inc.MonsantoNorthrup King CompanyPetaluma Hay AnalysisPGI AlfalfaPioneer Hi-Bred International, Inc.Rhone-Poulenc Ag. Co.Sandoz Agro, Inc.San Joaquin Valley Hay Growers AssociationSeedTec International, Inc.Sierra Testing ServiceSimplot SeedsSousa Ag ServiceThe Gooding Seed Co.Tri County Ag Service, Inc.TS&L Seed CompanyUnion Seed CompanyW-L Research, Inc.

ProductionDesign and Production Coordination:

Seventeenth Street StudiosDrawings: David Kidd and Lillian AlnevEditing: Toni MurrayPhotography: Except where noted, all black and white

photographs in this book were taken by Steve B.Orloff or provided by UC publications.

vi i n t e r m o u n t a i n a l f a l f a m a n a g e m e n t

I N T R O D U C T I O N 1

S. B. Orloff

C H A P T E R O N E

S I T E S E L E C T I O N 3

D. L. Lancaster and S. B. Orloff

Soil Factors 3

Topography 7

Irrigation Water 8

C H A P T E R T W O

S T A N D E S T A B L I S H M E N T 9

J. L. Schmierer, S. B. Orloff, and R. W. Benton

Seedbed Preparation 9

Preirrigation 11

Seeding 11

Planting Date 12

Seeding Strategies 15

Fertilizer Use 16

Irrigation 16

Weed Control 16

Companion Crops 17

Seed Inoculation 17

Fungicidal Seed Coatings 17

Timing of the First Harvest 18

C H A P T E R T H R E E

V A R I E T Y S E L E C T I O N 19

H. L. Carlson

Yield 19

Stand Persistence 19

Fall Dormancy 20

Pest and Disease Resistance 21

Hay Quality 23

Sources of Information 23

Interpreting Yield Trial Results 24

Varieties, Brands, and Blends 24

Seed Price 24

C H A P T E R F O U R

I R R I G A T I O N 25

S. B. Orloff, H. L. Carlson, and B. R. Hanson

Water Storage 25

Irrigation Scheduling 27

Adjustments to Achieve Uniformity and Efficiency 35

Application Rate 36

System Design Requirements 38

Irrigation System Improvements 38

Irrigation Strategies for Limited Water Supplies 40

c o n t e n t s vii

C H A P T E R F I V E

F E R T I L I Z A T I O N 41

R. D. Meyer, D. B. Marcum, and S. B. Orloff

Essential Plant Nutrients 41

Diagnosis of Nutrient Deficiencies 42

Correction of Nutrient Deficiencies 44

Record Keeping 49

C H A P T E R S I X

W E E D S 51

J. L. Schmierer and S. B. Orloff

Weed Biology 51

Weed Control 53

Weed Control in Seedling Alfalfa 53

Weed Control in Established Alfalfa 58

Summer Annual Weeds 61

Perennial Weeds 62

The Economics of Chemical Weed Control 63

C H A P T E R S E V E N

I N S E C T S 65

S. B. Orloff and R. W. Benton

Insect Identification 65

Alfalfa Weevil 66

Aphids 68

Caterpillars 69

Cutworms 70

Clover Root Curculio 70

Blister Beetles 71

Grasshoppers 71

Thrips 72

C H A P T E R E I G H T

N E M A T O D E S 73

H. L. Carlson and B. B. Westerdahl

Stem Nematode 73

Root-Knot Nematode 74

Root-Lesion Nematode 74

Nematode Detection and Identification 74

Control 75

C H A P T E R N I N E

D I S E A S E S 77

R. M. Davis, S. B. Orloff and K. D. Marshall

Damping-Off Diseases 77

Root and Crown Rots 79

Foliar Diseases 80

Wilt Diseases 81

C H A P T E R T E N

V E R T E B R A T E P E S T S 85

S. B. Orloff, T. P. Salmon, and W. P. Gorenzel

Pocket Gophers 85

Ground Squirrels 89

Meadow Mice 91

Deer and Antelope 92

K E Y T O P L A N T S Y M P T O M S 95

C H A P T E R E L E V E N

H A R V E S T M A N A G E M E N T 103

S. B. Orloff and V. L. Marble

Alfalfa Growth and Root Reserves 103

The Effects of Time of Cutting 103

viii i n t e r m o u n t a i n a l f a l f a m a n a g e m e n t

Selection of a Cutting Schedule 106

Cutting Height 107

Fall Harvest Management 107

C H A P T E R T W E L V E

H A Y C U R I N G , B A L I N G , A N D S T O R A G E 109

S. B. Orloff

Hay Curing 109

Baling and Storage 112

C H A P T E R T H I R T E E N

Q U A L I T Y A N D Q U A L I T Y T E S T I N G 117

S. B. Orloff and V. L. Marble

What Is Quality? 117

Quality Requirements 118

Factors Affecting Quality 118

Hay Evaluation 119

C H A P T E R F O U R T E E N

G R A Z I N GM A N A G E M E N T 127

R. R. Gildersleeve

Dormant-Season Grazing 128

Grazing as a Substitute for Cutting 128

Rotational Grazing during the Growing Season 129

Agronomic Practices 130

Animal Management Concerns 130

C H A P T E R F I F T E E N

M A N A G E M E N T A N D R E P L A C E M E N T O F D E P L E T E D S T A N D S 133

S. B. Orloff and D. H. Putnam

Evaluating Old Stands 133

Understanding Management Options 134

Stand Extension 135

Stand Replacement 137

c o n t e n t s ix

I N T RO D U C T I O NSteve B. Orloff

�lfalfa (Medicago sativa L.) is calledthe Queen of Forages. There is littlewonder why this crop has acquired

such a prestigious reputation. Not only is it the oldestcultivated forage crop, but it is also one of the mostpalatable and nutritious: Alfalfa is rich in protein, vit-amins, and minerals. When cut prior to bloom, it islow in fiber and high in energy. Because of its superiornutritional quality, alfalfa is the primary componentin the dietary ration of dairy cattle and is an impor-tant feed for horses, beef cattle, sheep, and milkinggoats. Alfalfa has a very high yield potential comparedwith that of other forage crops. It is an integral com-ponent of many crop rotations because of its ability tofix nitrogen, improve soil structure and tilth, and con-trol weeds in subsequent crops.

Alfalfa is the most popular and important foragecrop grown in California. It is produced on approxi-mately 1 million acres, or about 1 out of 8 eight irri-gated acres in the state. The intermountain counties ofSiskiyou, Shasta, Modoc, Lassen, Plumas, Sierra,Inyo, and Mono account for about 15 percent of thestate’s acreage and produce approximately 10 percentof the total crop. Alfalfa assumes a more prominentrole in the Intermountain Region than in other alfalfa-production areas of California because there are fewrotation crops in the area. Alfalfa is the most exten-sively grown crop in the Intermountain Region, aswell as the crop with the highest gross receipts.

The intermountain portion of Northern Californiahas unique environmental conditions that set it apart

from other alfalfa-production areas of the state.Actually, the intermountain area has more in commonwith neighboring states than with the rest ofCalifornia. Alfalfa is produced in high-elevation val-leys (from 2,500 to 5,000 feet) scattered throughoutthe intermountain area. Each valley has distinct physi-cal and climatic characteristics due to differences in el-evation and topography. Most soils of the region wereformed from alluvium derived primarily from vol-canic rock. Despite having a similar origin, great dif-ferences in soil properties exist between productionvalleys, within individual valleys, and even withinfields. Soils range in texture from loamy sands toheavy clay loams. Organic matter content varies fromless than 1 percent to more than 12 percent in theTulelake Basin. Irrigation water is supplied from lakes,rivers, and wells. Most alfalfa is sprinkler-irrigated(primarily by wheel lines and center pivots); however,flood irrigation is used in some of the more level val-leys with heavier soils.

Alfalfa is produced under dryland conditions insome valleys, but these areas represent a minor portion

1

of intermountain production acreage. The most dis-tinctive characteristic common to all intermountainareas is the short growing season (90 to 160 days).Coupled with the short growing season are large fluc-tuations in temperature, both from day to night andfrom summer to winter. Weather during the growingseason is generally warm during the day and cool atnight. However, below-freezing temperatures canoccur any night of the year in many of these produc-tion areas.

Climate has a profound effect on alfalfa produc-tion. Because of the climate in the IntermountainRegion, dormant varieties of alfalfa (those with a falldormancy rating from 2 to 4) prevail there. Growerscan obtain two to four alfalfa cuttings between Mayand September (three is the most common number).Annual hay production averages 5 tons, though yieldsof 8 tons per acre or higher have been obtained onmore productive soils under good management. Totalseasonal production is relatively low, but individualcuttings of 2 to 3 tons per acre are common. Stand lifeis long—typically 6 to 8 years.

The Intermountain Region is known for high-qual-ity alfalfa hay, which is sometimes called mountainhay. Its quality is commonly attributed to the shortgrowing season and cool night temperatures. For mostof the year, intermountain alfalfa grows more slowlythan that in warmer areas; therefore, it generally has ahigher leaf-to-stem ratio and a lower fiber content. Itis used locally as cattle feed and trucked to dairiesthroughout much of California and western Oregon.

Nearly all alfalfa is produced as hay, with very littlegreen chop or silage production.

Although the intermountain environment is advan-tageous for some aspects of alfalfa production, it cre-ates some serious challenges. Because of the short andrelatively cool growing season and cold winters, dis-eases and insects are not as great a problem as in otherareas. Because of fewer cuttings per season, summerannual grasses are not as serious as in the CentralValley and low desert areas of California. However, be-cause of the long stand life and limited rotation cropoptions, perennial weeds are particularly troublesome.Rodent pests are frequently a severe problem for thesame reasons. Climatic conditions are conducive toproduction of high-quality hay, but late- and early-season frosts are a constant threat. Rain damage iscommon during any cutting.

Successful alfalfa production in the IntermountainRegion requires a thorough understanding of all as-pects of crop management. The intent of this manualis to provide growers, advisors, and consultants in-volved in the alfalfa industry with a comprehensiveguide to alfalfa production and management in theIntermountain Region. Contributors were Universityof California Farm Advisors and Specialists. We haveattempted to assemble into one publication the mostcurrent information and recommendations on allareas of alfalfa management, including stand establish-ment, fertilizer use, irrigation, pest management, har-vesting, forage quality, grazing, and management ofdepleted stands.

2 i n t e r m o u n t a i n a l f a l f a m a n a g e m e n t

3

C H A P T E R O N E

S I T E S E L E C T I O NDonald L. Lancaster and Steve B. Orloff

�lfalfa can be grown on a variety ofsites in the Intermountain Regionof California. Since site conditions

often limit both yield and profit potential, a growershould pay particular attention to site selection. Somesite limitations can be overcome or reduced, but thecost may be high, affecting future profitability. If siteconditions are poor, alfalfa production may beunprofitable even under optimum management.

When selecting a site for alfalfa production, consid-er the physical and chemical properties of the soil, thelikelihood of waterlogging, the topography, and thequantity and quality of available irrigation water(Table 1.1).

When alfalfa is grown on sites that provide adequaterooting depth, nutrition, aeration, and water, and donot present excess salts or alkali problems, growersusing good management practices can produce hayyields of 6 to 8 tons per acre. However, greater man-agement skill is required to achieve profitable alfalfaproduction on marginal or undesirable sites. Remem-ber, the better the site, the higher the potential yield.

S O I L FA C TO R S

The geologic history of intermountain California iscomplex. Consequently, within a single 40-acre fieldmay be several different soil types. As the first step indetermining the suitability of a site for alfalfa produc-tion, learn the soil types found there by consulting soil

surveys. Published by the United States Department ofAgriculture Natural Resources Conservation Service,these surveys contain soil maps to assist growers inidentifying soil units, and include information on tex-ture, water-holding capacity, depth, drainage, andinfiltration rate. If the survey indicates that the sitemay have promise, have the soil and water analyzed.Do this before planting alfalfa on the site. Informationon soil sampling methods is presented in chapter 5.

Physical Properties

Soil textureThe term soil texture refers to the relative proportionof sand, silt, and clay in soil. Soil texture affects thewater-holding capacity and infiltration rate (the rate

at which irrigation water will enter the soil profile).Clay holds the most water; sand allows the fastestwater infiltration.

Alfalfa can be successfully produced on a widerange of soil textures, but sandy loam to clay-loamsoils are preferred. These soil types provide the bestcombination of water holding and water infiltrationfor alfalfa. Sands and loamy sands have such lowwater-holding capacities that fields must be irrigatedevery few days, a task that is difficult with most irriga-tion systems (except center pivot or linear move sys-tems). Alfalfa production on fine-textured clay soilscan be equally difficult. In these soils, water infiltra-tion and drainage are extremely slow. Aeration may bepoor because the small pore spaces associated with finesoils limit the diffusion of oxygen to plant roots,impairing root growth.

Rocky soils are common in the IntermountainRegion. Soils with numerous rocks near the surface arenot well suited to cultivation and often damage har-vest equipment. Avoid them whenever possible.

Depth and profileThe soil provides a rooting medium through whichthe alfalfa draws water and nutrients. The deeper thesoil, the more water and nutrient storage capacity the

site provides. To find soil profile problems, use a back-hoe to dig several evaluation pits in a potential field(Figure 1.1). Each pit should be at least 4 feet deep.

An ideal site has deep, uniformly textured soil withno drainage or salt problems. Under ideal conditions,alfalfa roots will extend 6 to 12 feet deep or more.Unfortunately, because of the geology of theIntermountain Region, many soils are not that deep. Tobe suitable for alfalfa production, a site should providea minimum of 3 feet of unrestricted rooting depth.

Like shallow soils, restrictive subsurface layers limitalfalfa production. The most common problems inthe Intermountain Region are hardpans, claypans,sand and gravel lenses, and stratified or layered soils.These reduce alfalfa yields because they present a bar-rier to root penetration or inhibit water infiltrationand drainage.


Table 1.1. Characteristics of ideal, marginal, and undesirable sites for alfalfa production.

U N I T O FC H A R A C T E R I S T I C M E A S U R E I D E A L M A RG I N A L U N D E S I R A B L E 1

Soil texture Sandy loam–clay loam Loamy sand, silty clay Sand, clay

Soil depth ft >6 3–6 <3

Soil chemistry2

pH 6.3–7.5 5.8–6.3 and 7.5–8.2 <5.8 or >8.2

ECe mmho/cm 0-2 2–5 >5

ESP % <7 7–15 >15

Boron mg/L 0.5–2.0 2–6 >6

Frequency ofwaterlogging or high water table Never Only during dormant period Sometimes during periods

of active growth

Slope Nearly level Slightly sloping to 12% slope >12% slope

Water supply gpm/acre >8 5.5–8 <5.5

Water quality

ECw mmoh/cm <1.3 1.3–3.0 >3.0

SAR <6.0 6.0–9.0 >9.0

Boron mg/L <0.5 0.5–2.0 2.0–6.0

Note: These categories are approximate and should be modified when warranted by experience, local practices, special conditions, or irrigation method.1. These sites are considered unsuitable for profitable alfalfa production unless reclaimed or specialized management is employed. 2. Values are based on saturated paste pH and saturated paste extract concentrations.

A site should provide a minimum of 3 feet of

unrestricted rooting depth.

s i t e s e l e c t i o n 5

Soil profile problems are not limited to compactedlayers—abrupt changes in texture within the soil pro-file can have a similar effect. A clay layer within asandy loam soil or a layer of sand within a loam orclay-loam soil can prevent root penetration and soilwater movement. An abrupt change in soil textureimpedes the downward movement of water evenwhen water is moving from a clay soil into a sandylayer. Water movement into a different textural classdoes not occur to any appreciable degree until thelayer above is saturated. Consequently, a zone of pooraeration often occurs at the interface between differ-ent layers and can even result in a temporarily perchedwater table. The greater the change in textural classand the more abrupt the change, the greater the effect.

Deep tillage can help reduce, but usually can noteliminate problems associated with hardpans, clay-pans, and layered soils. Deep ripping is effective toresolve hardpan problems, since a fractured hardpanwill not re-cement itself. However, ripping alone isnot enough to solve a claypan or layered-soil problem.These problems are only solved by mixing soils to adepth below the restrictive layer. This is usuallyaccomplished with a moldboard or slip plow. Majorphysical modification of soils is expensive (often inexcess of $200 per acre), and alfalfa production sel-

dom justifies the cost. When possible select an alterna-tive site, free of restrictive subsurface layers.

Waterlogging and Fluctuating Water Tables

Some areas of the Intermountain Region are formerswamps or lakes and are subject to fluctuating watertables and intermittent flooding. During years ofabove-average precipitation, the water table level maybe well within the root zone of alfalfa. Alfalfa does nottolerate wet soil conditions during periods of activegrowth: perched or fluctuating water tables in the rootzone can severely reduce yields and stand life. Oxygendepletion in the root zone and diseases of the root andcrown (such as Phytophthora root rot) often occurunder excessively wet conditions.

An intermittent, or fluctuating, high water table isusually more damaging than a stable high water table.With a stable high water table, the alfalfa roots arerestricted to the well-aerated soil above the high watertable. However, with a fluctuating water table, rootsmay grow below the high water table level when con-ditions are favorable, only to become damaged whenthe water table rises. The damage that occurs fromwaterlogging depends on the time of year when water-logging occurs and its duration. Waterlogging is farmore serious when it occurs during the growing sea-son than when alfalfa is dormant. Furthermore, thelonger waterlogging persists and the warmer the tem-perature, the greater the injury to the crop.

Deep tillage can improve internal drainage in somesoils. Precise field leveling and drainage tile may alsohelp correct waterlogging problems, but the resultingincrease in alfalfa production may be insufficient torecover the costs. Avoid sites with waterlogging or afluctuating high water table.

Figure 1.1. Use a backhoe to dig several evaluation pits in a poten-tial field to determine the soil depth and to detect soil profile problems.

Alfalfa does not tolerate wet soil conditions during periods of active growth.

DO

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Chemical Properties

FertilityThe parent material of a soil largely determines itsmineral content and fertility. Most areas of theIntermountain Region are naturally deficient in sulfurand phosphorus. Potassium, boron, and molybdenumare also deficient in some sites. These nutrient defi-ciencies are easily corrected through proper diagnosisand fertilizer application (see chapter 5); they do notlimit site selection.

pHSoil pH affects nutrient availability and can indicateproblems with soil structure. Maximum nutrientavailability for most crops occurs when pH values arebetween 6.0 and 7.0. However, higher pH values (6.3to 7.5) are recommended for alfalfa productionbecause they favor activity of nitrogen-fixingRhizobium bacteria. Soils with pH values below 6.0are unsuitable; lime them before planting, particularlyif pH decreases with increasing soil depth. On theother hand, soil pH values above 8.2 indicate excesssodium. High-pH sites are relatively unproductiveunless reclaimed (Figure 1.2).

Salinity and Sodicity Problems with excess soil salt (saline soils) and sodium(sodic soils) occasionally occur in the IntermountainRegion. Soils formed in enclosed basins under low-rainfall or desert conditions are often saline. Also con-ducive to high salt concentrations are high watertables in which salts rise because of the upward (capil-lary) movement of water. Similarly, irrigation waterhigh in soluble salts contributes to soil salinity.

Alfalfa is moderately sensitive to salt. High salt maybe toxic and reduce water availability. Visual indica-tors of excess salt include slick spots, white or blackcrusts on the soil surface; marginal leaf burn; and thepresence of salt-tolerant weeds. Laboratory analysis ofsoils is required to confirm visual symptoms and todetermine the type and degree of salinity. Carefullysample fields at different depths throughout the rootzone when salinity is suspected.

Soil salinity is measured by determining the electri-cal conductivity of the soil extract (ECe ). Salts con-duct electricity; therefore, the higher the electrical

conductivity of the soil extract, the greater the salinityof the soil. ECe values above 2.0 millimhos per cen-timeter (mmho/cm) can suppress alfalfa yields,depending upon the specific ions in the soil-water


Before it is possible to reclaim any saline or sodicsoil, a grower must have

1. an ample supply of quality waterReclamation requires a supply of irrigation watersufficient to leach excess salts below the rootzone. Until the soil is reclaimed, apply morewater than is necessary to satisfy the needs ofalfalfa. The extra water carries harmful saltsbelow the root zone, where they are less likely toinjure the crop.

2. good drainageBoth surface and internal drainage must be ade-quate. Water must pass into and through the soilto carry away salts present in the soil or releasedduring reclamation. Salts are not washed off thesoil surface, but through the soil below the rootzone. Therefore, soil reclamation cannot occurwithout adequate drainage to at least the depthof the root zone. Deep ripping or installation ofdrainage tiles may be required to provide accept-able internal drainage in some sites.

3. a source of calciumReclamation of sodic (not saline) soils requiresthat calcium replace the sodium that is leachedoff soil particles. If calcium carbonate is presentin the soil, sulfur-containing soil amendmentscan be used to free up the calcium. To soils low incalcium apply a calcium source, such as gypsum.

4. adequate financing to complete the jobReclamation requires a considerable investment.Unless you have adequate finances to completethe job, reclaiming salt-affected soils may not bea profitable venture.

5. patienceComplete reclamation may take many years.Initially, growers must be content with improvedland rather than an actual cash return from cropproduction.

Adapted from Mueller. 1992. Site Selection. In: Central San JoaquinValley Alfalfa Establishment and Production.

Figure 1.2. Soil reclamation requirements.

solution. Alfalfa suffers a 10 percent yield reductionwhen soil salinity levels reach approximately 3.4mmho/cm. In general, soils with ECe values above 5.0should be avoided or reclaimed prior to planting alfal-fa. If drainage is adequate, saline soils can be reclaimedby deep leaching. Water in excess of crop needs mustbe applied for deep leaching to occur. This is most eas-ily accomplished by reclaiming the soil prior to plant-ing alfalfa or by applying water during the dormantseason, when alfalfa is not actively growing.

Excess sodium can be a significant yield-limitingfactor. High sodium levels cause clay particles to dis-perse. This degrades soil structure; the soil surfaceseals and water infiltration slows. Soils with anexchangeable sodium percentage above 15 are consid-ered sodic. This means that more than 15 percent ofthe exchange sites (negatively charged positions onsoil particles that hold onto positively charged ele-ments and compounds) are occupied with sodiumrather than beneficial elements such as calcium, mag-nesium, and potassium. When this condition occurs,a laboratory analysis can determine the gypsumrequirement of the soil. Gypsum requirement refers tothe amount of calcium required to displace sodium onthe exchange sites. Sulfur can be used instead of gyp-sum to reclaim soils that are high in calcium carbon-ate. After an amendment has been applied andsodium replaced with calcium, the displaced sodiummust be leached below the alfalfa root zone.

Avoid sites that are adversely affected with excesssalts or sodium. The reclamation process usuallyrequires several years and, in the case of sodic soils, asubstantial investment in soil amendments.Subsurface drainage systems may also be required toeffectively reclaim a site for sustainable economicalalfalfa production.

Boron Some sites present growers with boron problems. Inthe Intermountain Region boron deficiency is muchmore common than boron toxicity. Fertilizers can cor-rect boron deficiency (see chapter 5). Because alfalfais highly tolerant of boron, boron toxicity is rarely aproblem in alfalfa fields in the Intermountain Region.When it occurs, however, it can be difficult to resolve.Boron is far more difficult to leach than sodium orother salts. Boron toxicity is usually associated withhigh concentrations of boron in the irrigation water.Changing the water supply may help correct the prob-lem. High boron levels in soil are difficult to lower;doing so takes large quantities of water and manyyears. Fortunately, boron toxicity problems are notobserved in alfalfa until soil boron levels exceed 6 mil-ligrams per liter in saturated paste extract.

TO P O G R A P H Y

Level or nearly level land facilitates irrigation andwater penetration. Water accumulation in low spotscan “drown out” alfalfa. Uneven or undulating fieldsmay require extensive land leveling. This results inmajor cut and fill areas, which often create additionalproblems. Areas where major cuts have been made areusually less productive because much of the topsoilhas been removed and the soil may be shallower thanin surrounding areas. The productivity of cut areasmay not match that of the rest of the field until theyhave been farmed for several years. Also, significantsettling may occur in fill areas, making additional lev-eling necessary. To alleviate some of these problems, aswell as the salinity problems that commonly occur innew fields, produce an annual crop such as smallgrains before planting alfalfa.

Both topography and soil texture should determinethe type of irrigation used. Use sprinkler irrigation oncoarse-textured soils or moderately sloping land. Evenwith sprinkler irrigation systems, the amount of slopethat can be tolerated is limited, depending on the soil-water infiltration rate. In most cases, avoid slopes inexcess of 12 to 15 percent.

s i t e s e l e c t i o n 7

A water supply of at least 7 to 8 gallons per minute is needed for each acre of alfalfa.

I R R I G AT I O N WAT E R

When selecting a potential site for alfalfa production,be sure that there is an adequate supply of quality wateravailable for season-long irrigation. Both quantity andquality of irrigation water can limit alfalfa yields.

Quantity

Insufficient irrigation water is perhaps the most com-mon site limitation in the Intermountain Region. Manyfields have been planted with inadequate irrigation sys-tems, pump capacity, or water supply. Peak water use ofalfalfa, approximately 0.30 inches per day, occurs dur-ing July (see chapter 4). To meet peak water needs andcompensate for inefficiencies in the irrigation system, awater supply of at least 7 to 8 gallons per minute isneeded for each acre of alfalfa. The precise amountdepends on the climate of the area and the uniformityof water application. Failure to meet peak water needsresults in reduced seasonal yields and profits.

Quality

Poor water quality is occasionally a problem in theIntermountain Region. Water from underground wellsmay contain excess salt. Excess boron is a problem in

some geothermal wells in the region. Some surfacewater sources contain excess colloidal clays, salts, orweed seeds that can present management and stand-life problems. See Table 1.1 for guidelines about waterquality. Toxicities due to foliar absorption of sodiumand chlorides can occur with sprinkler irrigation. Thisis most common during periods of very low humidityand high winds.

Little can be done to improve irrigation water quali-ty. In fact, soil reclamation efforts are unproductive ifirrigation water quality is poor. The only cost-effectivemethod of dealing with poor irrigation water is to findan alternative water source or blend the existing waterwith higher-quality water.

A D D I T I O N A L R E A D I N G

Ayers, R. S., and D. W. Wescot. 1985. Water quality for agricul-ture. Irrigation and Drainage Paper No. 29. Rome: UnitedNations Food and Agriculture Organization.

Frate, C., S. Mueller, and R. Vargas. 1992. Central San JoaquinValley alfalfa establishment and production. Fresno, CA:University of California Cooperative Extension.

Marble, V. L. 1990. Factors to optimize alfalfa production in the1990s. Proceedings, 20th California Alfalfa Symposium, 4–45.December 6–7, Visalia, CA.

Richards, L. A., ed. 1954. Diagnosis and improvement of saline andalkali soils. Handbook No. 60. U.S. Department ofAgriculture, Washington, D.C.


9

C H A P T E R T W O

S TA N D E S TA B L I S H M E N TJerry L. Schmierer, Steve B. Orloff, and Roger W. Benton

�rofitable alfalfa production is contingentupon establishment of a dense vigorousstand. Proper stand establishment is espe-

cially important in the Intermountain Region, wherealfalfa fields may remain productive for 5 to 8 years orlonger. Poor stand establishment can reduce theprofitability of alfalfa by lowering yields, diminishingstand life, and reducing the nutritional quality of thehay. Mistakes made during stand establishment can-not usually be offset later.

S E E D B E D P R E PA R AT I O N

Inadequate seedbed preparation is a common cause ofstand establishment failure. The objectives of seedbedpreparation are to loosen the soil to remove anyimpediment to root growth, to level the field fordrainage and ease of harvest, and to firm and smooththe soil surface for optimum crop emergence. This isaccomplished through primary tillage (deep plowingor ripping); land leveling; and secondary tillage,which breaks up clods and firms the soil.

Primary Tillage

Alfalfa requires well-drained, relatively deep soil (aminimum of 3 to 4 feet) for maximum production.Physical or chemical limitations caused by hardpans,stratified soils, or salts can restrict rooting depth,which leads to decreased productivity and lower yield.Soil compaction occurs from equipment traffic, espe-cially when it takes place on wet soils and when thecrops transported are heavy, as are potatoes or sugarbeets. Deep tillage can reduce compaction.

Several deep-tillage implements are used in alfalfaseedbed preparation: a ripper, or subsoiler; a mold-board plow; and a slip plow. A ripper is the most com-monly used implement to alleviate compaction. Forbest results, work when the soil is dry and rip belowthe depth of the compacted layer. Ripping wet soilsdoes not fracture compacted layers. Space the shanksno more than 3 feet apart. Ripping in one direction athalf the spacing results in more of the soil being fractured than cross ripping—that is, using 20-inchcenters in one direction is more effective than using40-inch centers in two directions. The duration of thebeneficial effects of ripping varies depending on the

soil type and the nature of the compaction problem,but fields should ordinarily be ripped prior to eachalfalfa planting. In some cases ripping can be donewell in advance of alfalfa seeding. For example, priorto a spring planting, rip fields in the fall. Rip fields in acereals-alfalfa rotation prior to planting the grain crop.Ripping shatters compacted layers but does not mixthe soil, so the beneficial effects of ripping may beshort-lived in layered soils (soils with distinct changesin soil texture with depth).

A moldboard plow can also be used to alleviatecompaction problems. It is particularly beneficial inlayered soils, because plowing inverts and mixes thesoil. Plowing can be a useful way to remove old alfalfastands, bury weed seeds and plant debris, and incor-porate fertilizer deep into the soil. However, plowingcan sometimes bring less-desirable soil to the surfaceand is especially problematic in rocky fields. Any soilrequires extra tillage or time to firm up or settle afterplowing. In most Intermountain Region soils, anexcellent seedbed can be prepared without plowing.

The proper type and degree of deep tillage can bedifficult to ascertain. No single “recipe” is appropriatefor all locations. An understanding of the soils and aknowledge of crop history are great aids in evaluatingthe need for deep tillage. Prior to removing a stand usea backhoe to determine the distribution of roots in thesoil profile; root distribution indicates soil stratifica-tion or impermeable layers. The economics of deeptillage can be difficult to predict. Deep-tillage imple-ments have high horsepower requirements, so deeptillage can be very expensive—in excess of $200 peracre. Fortunately, deep tillage is not necessary for mostfields in the Intermountain Region. However, rippingto moderate depths, 20 to 32 inches, is usually cost-effective and recommended to reduce compactionfrom preceding crops.

Land Leveling

Leveling the field is important. The degree of levelingnecessary depends on the irrigation system and soiltype. With sprinkler irrigation, low spots need to befilled and leveled so that water does not pond anddrown the alfalfa. More extensive leveling is requiredfor fields with flood-irrigation systems.

Before the advent of laser leveling, correct cut andfill as well as the proper field slope were difficult to

attain. Laser leveling is expensive, but it is by far thepreferred method when flood irrigation is used. Laserleveling may be done in two stages. The rough levelingmay be done after primary tillage. After irrigation bor-ders are formed, the area between borders can be laser-leveled to attain a precise level and slope. Laserleveling between borders is also a common practice inolder, previously leveled fields that are being plantedto alfalfa.

Secondary Tillage

The field should be disced, harrowed, floated, andpacked to form a firm, clod-free seedbed that is nei-ther powdery nor fluffy (Figure 2.1). It should be firmenough so that a heel print in the prepared soil is notmore than 1⁄2 inch deep. Poor establishment is likely ifthe surface is not well compacted prior to seeding. Arelatively clod-free seedbed prevents excess air space,permits good seed-soil contact, allows uniform plant-ing depth, and improves moisture availability to theseed. Take care not to overwork heavy soils:Overworking will increase their undesirable tendencyfor surface crusting.


Figure 2.1. The ideal seedbed should be firm, not powdery or fluffy,and clod-free.

CO

UR

TE

SY F

OR

D N

EW

HO

LL

AN

D

s t a n d e s t a b l i s h m e n t 11

P R E I R R I G AT I O N

Alfalfa can be seeded into moist soils or seeded into drysoils and then irrigated. Planting into moisture can beaccomplished by either preirrigating before planting orby preparing the seedbed in the fall and taking advan-tage of winter precipitation to provide moisture. Theadvantages of planting into moist soils are that themoisture has usually melted the clods and, if the mois-ture is uniform, alfalfa seeds can germinate uniformlyand quickly. Also, keeping up with irrigation is easierwhen starting with a full soil-water reservoir. Contact-type herbicides or shallow cultivation can be used tocontrol weeds that emerge prior to planting.

Despite these advantages, the time required forseedbed preparation, irrigation, surface drying, spray-ing for weed control, and then planting deters manygrowers from preirrigation. Preparing the seedbed,planting, and irrigating is much simpler. However, adry planting system can be less forgiving. The growermust take great care to meet the water requirements ofthe young crop. Weed populations are usually higherin fields that have not been preirrigated, makingpostemergence weed control more difficult.

S E E D I N G

Seeding Depth

Seed placement is critical. More stand establishmentfailures probably relate to seeding too deep than toany other single factor. Seeding depth should notexceed 3⁄8 inch, except for sandy soils, where 5⁄8 inch isacceptable. Seeding deeper than this can reduceseedling emergence considerably (Table 2.1).

Seeding Methods

Various implements are used to plant alfalfa, but allbasically involve either broadcasting or banding(drilling) the seed. Each method presents advantagesand disadvantages. Factors to consider when selectinga seeding method include cost, time, equipment avail-able, and uniformity of seed distribution. Adequatealfalfa stands can be established using either method.Firming the seedbed after planting is an importantpart of seeding. It ensures the seed-soil contact neces-sary to prevent desiccation of the emerging alfalfaseedling. Cultipacking or ring rolling once after seed-ing is usually sufficient in broadcast seedings; culti-packing twice can be beneficial on coarse-texturedsoils. Press wheels or a cultipacker works well indrilled seedings.

BroadcastingCompared to banding, broadcast seeding is generallyfaster and distributes seed more uniformly. A disad-vantage of broadcast seeding is that uncovered seedremains on the soil surface. However, the amount ofuncovered seed is considered insignificant. Several sys-tems are used to broadcast alfalfa seed. A cultipackerseeder such as a Brillion seeder has been used withexcellent results (Figure 2.2). A Brillion seeder dropsseed between double corrugated rollers. The leadingroller breaks clods and firms the soil prior to seeding.The trailing roller splits the ridges made by the firstroller, covering and packing the seed. Seed can also besuccessfully broadcast by using an air-flow ground

Table 2.1. Emergence from different seeding depths.

DEPTH (IN.) % EMERGENCE1

1⁄4–1⁄2 60

1 48

2–21⁄2 2

Source: R. Sheesley1. Emergence from different depths can vary with soil type—that is, poorer

emergence results from deeper depths with a heavy soil, in contrast to asandy soil.

Figure 2.2. A Brillion seeder is often used with excellent results tobroadcast alfalfa seed.

VE

RN

MA

RB

LE

applicator, fluid or suspension seeding techniques,aerial application, or the small seed attachment of agrain drill, which allows seed to fall out of the seedtubes and scatter on the ground. Aerial seeding isuncommon in the Intermountain Region. Whenused, increase the seeding rate by 2 to 4 pounds peracre to compensate for losses and nonuniformity.

BandingA standard grain drill is typically used to band, ordrill, alfalfa. Nearly all the seed is incorporated andcovered when alfalfa seed is drilled. Phosphorus fertil-izer can be banded with the seed at the time of seed-ing, another advantage of this seeding method. Inaddition, drilling disturbs soil less than does broad-casting, so drilling conserves soil moisture. This is par-ticularly important when growers rely on rainfall forcrop emergence. The primary disadvantage of drillingalfalfa seed relates to distribution. The distancebetween alfalfa seed rows is typically 6 to 7 inches.This is a particular problem when there is a planterskip, doubling the distance between rows to 12 to 14inches. Some growers drill in two directions to over-come this problem.

Seeding Rates

A wide range of seeding rates can be acceptable pro-vided the seedbed was properly prepared. Twentyalfalfa seedlings per square foot constitutes an ade-quate stand. One pound of alfalfa seed spread evenlyover an acre equates to approximately 5 seeds persquare foot (4 pounds per acre equals 20 seeds persquare foot). Although these figures suggest extremelylow seeding rates are feasible, this is not the case.Typically, only 60 percent of the seeds germinate andemerge; 60 percent of emerged seedlings may die dur-

ing the first year. Under ideal conditions, adequatestands have been established with seeding rates as lowas 12 to 15 pounds per acre. To compensate for less-than-ideal conditions and unforeseen weather, theseeding rate recommended for irrigated fields is 15 to20 pounds per acre when drilling and 20 to 25 poundsper acre when broadcasting. An extra few pounds ofseed is generally not too costly and is cheap insuranceagainst less-than-optimum seedbed and weather con-ditions. Seeding rates higher than these are excessive.Because of self-thinning, a 1-year-old alfalfa standseeded at an excessive rate would not likely be any dif-ferent than a 1-year-old stand seeded at the recom-mended rate.

Seed dryland alfalfa at 8 to 10 pounds per acre.Higher seeding rates waste seed because dryland con-ditions cannot support as many plants per square footas can irrigated fields.

P L A N T I N G D AT E

Factors to be considered when determining plantingdate include weather (primarily temperature and thelikelihood of rainfall), cropping pattern, harvest dateof the preceding crop, water availability, irrigationmethod, weed pressure, and the time of year whenenvironmental conditions are optimum for crop emer-gence and seedling development. No single plantingdate satisfies all the criteria. Advantages and disadvan-tages of each time period must be weighed to decidethe most appropriate date (Table 2.2). Actual seedingdates vary depending on the intermountain produc-tion area (Figure 2.3).

Spring

Spring planting dates vary considerably within theIntermountain Region. Planting can begin as early asthe last week in February in areas such as ShastaValley; they can be as late as the end of May in higher-elevation areas. The likelihood of a damaging frostdelays the starting date for spring planting. Alfalfa isextremely cold tolerant at emergence. However, plantsare frost sensitive when they have two trifoliolateleaves, and may be killed by 4 or more hours exposure,at 26ºF (–3ºC) (Figure 2.4). After plants reach thethree-leaf stage, they can again withstand lower tem-


More stand establishment failures probably relate to seeding too deep than to any other single factor.

peratures. The main advantage of spring planting isthat spring rains may provide sufficient moisture forcrop emergence and reduce subsequent irrigationrequirements. This is particularly advantageous inflood-irrigated fields. It is difficult to flood-irrigateduring alfalfa establishment without causing soil ero-

sion and washouts. (A washout is when irrigationwater tears a seedling out of the soil.) The primary dis-advantages of spring planting are competition fromsummer annual weeds and first-harvest yields lowerthan those from fall plantings.


Table 2.2. Considerations in selecting a planting date.

ADVANTAGES DISADVANTAGES

January February March April May June July August September October

Spring Midsummer Late summer

Sierra Valley

Scott Valley

Shasta Valley

Butte Valley

Tulelake

Fall River Valley

Big Valley

Alturas

Honey Lake Valley

Surprise Valley

Madeline

Figure 2.3. Alfalfa planting dates for areas in the Intermountain Region.

Spring • Rainfall may be sufficient for crop emergence. (This is

especially important for flood-irrigated alfalfa fields.)

• Higher yield the seeding year than that from summer

planting.

• Reduced yields in seeding year (compared to fall seeding).

• Chance of damaging spring frosts.

• Weed competition. (Summer weeds may persist beyond

first cutting and contaminate subsequent cuttings.)

• Irrigation may be difficult during summer of first year (due

to limited root system).

Late summer • Nearly full production the year after seeding.

• Less weed competition: Many fall-germinating annual

weeds are killed by winter frosts; surviving winter annual

weeds will be removed in the first cutting.

• Alfalfa root and crown development over fall and spring

facilitate irrigation management the first year.

• Sprinkler irrigation needed for crop emergence.

• Likelihood of frost or heaving injury if planted too late.

• In higher-elevation areas climate may preclude harvesting

grain early enough to allow for timely alfalfa seeding.

• Frequent light irrigations required; many irrigation systems

are inadequate.

• Income lost from rotation crop or shorter production sea-

son for alfalfa.

• Competition from summer annual weeds.

• Low probability of killing frost.

• Rapid uniform emergence.

• Improved effectiveness of some broadleaf herbicides (such

as 2,4-DB).

Midsummer

leaflet

LEAF

seedgermination

emergencecotyledon

unifoliolate firsttrifoliolate

thirdtrifoliolate secondary stem early bud early bloom

Midsummer

Summer plantings are the norm for elevations around5,000 feet. Even in the lower valleys, planting duringthe warm summer months offers advantages. Warmtemperatures promote rapid and uniform emergenceand development of the young seedlings, and the dan-ger of a killing frost is very low. The broadleaf herbi-cide 2,4-DB works well under these conditions. Themajor disadvantage of summer planting is that hot dry weather in midsummer can make maintainingadequate soil moisture extremely difficult, and makefrequent irrigation necessary. An inadequate irrigationsystem or insufficient labor is an insurmountableobstacle to summer planting.

Fall

Fall planting in the Intermountain Region is moreappropriately called late-summer planting.Depending on elevation, early to late August is thebest time for a late-summer planting. Seeding at thistime offers significant advantages. Moderate tempera-tures favor rapid emergence and development of alfal-fa seedlings. Alfalfa plants seeded in late summercontinue to grow and develop over the fall and spring.By mid-spring, alfalfa plants are well established andthe result is a first-year yield similar to that from anolder stand and much greater than that from a springseeding. This is a major economic advantage. Theyield advantage is not limited to the first productionseason; it continues for several yeears after planting.


Figure 2.4. Alfalfa seedling growth and development. The twoleaves that first appear after emergence are called cotyledons or seed leaves. The next leaf is the unifoliolate leaf. The first true leaf is trifoliolate—that is, it has three leaflets.

Also, compared to spring-seeded alfalfa, alfalfa plantsseeded in late summer have a much better-developedroot system come summer. Consequently, it is easierto avoid moisture stress between irrigations during thehot summer months.

The risk of late-summer planting occurs when fieldsare planted too late (September or later in most areas).Planting should be completed at least 30 to 45 daysbefore the first killing frost (approximately 26ºF, or –3ºC). Harsh winter conditions can take a toll onimmature alfalfa seedlings. Freezing and ice formationcauses soil heaving in fine-textured soils, uprootingand killing alfalfa seedlings that have not developed anadequate root system. Larger, more-established plantsare better able to withstand these conditions.

The ability to seed alfalfa in late summer dependson the crop rotation sequence and weather. If alfalfafollows a late-harvested crop such as sugar beets orpotatoes, a late summer planting is not possible.However, late-summer alfalfa plantings following awinter or spring cereal crop are feasible. Winter cerealsor cereals grown for hay work best because they areharvested early enough to allow sufficient time to pre-pare fields for an August alfalfa planting. An Augustplanting is also feasible following spring cereals pro-duced for grain. Success depends on the harvest date ofthe grain, and the harvest date relates to the produc-tion area and weather conditions.

S E E D I N G S T R AT E G I E S

Several strategies have been developed to seed alfalfa inthe Intermountain Region. The best approachdepends on the area, soil type, and planting date.

Tillage Prior to Seeding

The most common technique for both spring and fallplantings is to perform tillage and seedbed preparationoperations just prior to planting. A technique thatworks well for spring plantings is to do primary tillagein the fall and final seedbed preparation in the spring.Soils are usually drier in fall than they are in spring, so

ripping in the fall is more effective. An early springplanting date is possible because growers are not delayedwaiting for spring soils to dry sufficiently to rip them.

Fall Tillage with Spring No-till Seeding

In spring, heavy soils are nearly impossible to prepare.An alternative in some areas is to prepare the land infall and let winter rains and freezing create a clod-freesurface (this has been done successfully in the ShastaValley). Emerged weeds can be sprayed with Roundup(glyphosate) herbicide prior to seeding. The seedbedwill generally be weed-free and the surface smooth andfirm. In warmer areas growers use no-till methods toplant alfalfa in late February. These growers prefer no-till drilled seeding because tillage dries out the surface,removing needed moisture in the surface layer. Thistechnique relies on soil moisture and spring rains forcrop emergence and early seedling development. Thefield does not usually require irrigation until the alfalfais a few inches tall and the threat of washouts fromflood irrigation has diminished.

Stubble Seeding

Seeding into stubble is a practice used by many growerswho have a crusting or wind erosion problem. It workswell for late-summer seedings when there is insufficienttime to cultivate the soil. Alfalfa seed is sown directlyinto the cereal stubble. Seedbed preparation, fertilizerapplication, and leveling all occur prior to cereal plant-ing. After the grain crop is harvested, the straw isburned or it is cut, raked, and baled. For stubble seed-ing, oat hay may be preferable because its stubble isshort—growers have no excess straw to remove. Also,volunteer grain is not usually a problem following anoat hay crop. But beware: If too much straw or stubbleis left in the field, providing winter cover for meadowmice, a severe pest problem can develop (see chapter10). When necessary, weeds can be controlled with afoliar herbicide prior to alfalfa emergence. A suitableseedbed is prepared by using a harrow or other tillageimplement (such as a Rotera tiller) to loosen soil and


allow seed incorporation. For stubble seeding, alfalfaseed can be broadcast or drilled.

F E RT I L I Z E R U S E

Adequately fertile soil is fundamental to successfulstand establishment. Soil fertility contributes toseedling vigor, which helps alfalfa compete with weeds.Analyze soil fertility prior to planting (see chapter 5).Phosphorus is commonly deficient and is particularlyimportant when establishing alfalfa. If soil is deficientin phosphorus, apply a 1- to 2-year supply at planting.The fertilizer can be broadcast and then disced or har-rowed. Banding phosphorus with or below the seedhas worked well for drilled seedings. This methodplaces the element where it is readily available to the

alfalfa, not the weeds. Furthermore, banded fertilizer isless likely to be bound in soil reactions than is broad-cast fertilizer.

The merit of applying nitrogen to alfalfa has beendebated for years. Although applying small amounts ofnitrogen at planting may increase seedling growth andvigor, it is not economical in most cases. As a generalguideline, when soil nitrate levels are greater than 15parts per million (ppm) and conditions favor effectivenodulation (soil pH of 6.2 to 7.5 and presence ofsufficient Rhizobium bacteria), nitrogen applicationdoes not result in economical yield increases. However,a yield increase may be expected when conditions fornodulation are poor, when soil nitrate levels are below15 ppm, or when organic matter content is below 1.5percent. A response to nitrogen fertilizer is more likelywhen soil temperatures are less than 60ºF (16ºC) forseveral weeks after planting. Under these circum-stances, a small amount (10 to 50 pounds per acre) ofnitrogen fertilizer is beneficial. A greater amountinhibits nodulation and delays crop development.Growers must be aware that applying nitrogen fertiliz-

er may promote weed growth. For this and other rea-sons, preplanting nitrogen applications should notexceed 20 pounds per acre.

I R R I G AT I O N

Proper irrigation of a new seeding is essential toachieving a dense healthy stand. The soil must remainmoist while alfalfa is germinating and during initialseedling development. Seedling alfalfa plants are not asresilient as established plants; seedlings should not bestressed, either with too much or too little water. Somegrowers let seedling alfalfa fields become dry, trying toforce roots to grow deeper. This is not a recommendedpractice; plant roots grow in the presence of water, notin search of it. Plant roots will not grow in dry soil.

The irrigation requirements of a seedling field obvi-ously depend on planting date. Rain may suffice for anearly spring seeding, but seeding after March is riskywithout the ability to irrigate. Growers that have toirrigate a new seeding should apply approximately 1inch of water per irrigation (a 3- to 4-hour set for mostwheeline irrigation systems). Assuming a 1⁄4 inch perday moisture loss due to soil evaporation and cropwater use, sprinkle every 4 to 5 days (for detail on irri-gation scheduling, see chapter 4). Do not overirrigate;damping-off diseases (chapter 9) that attack youngseedlings are greatly enhanced by excessively moistconditions.

W E E D C O N T RO L

The consequences of inadequate weed control in theseedling year can be devastating to the alfalfa stand andthe profitability of alfalfa production. Weeds competewith alfalfa for light, water, and nutrients and canreduce the vigor of seedling alfalfa. In cases of severecompetition, weeds can reduce alfalfa plant density tosuch a degree that the field has to be replanted. Someweeds can be toxic or unpalatable to animals and makethe first cutting unsalable.

Controlling weeds in the seedling year can get thealfalfa off to a fast, healthy start and reduce weed pres-sure in subsequent years. Deal with perennial weedsseveral seasons before planting alfalfa. Proper weedcontrol in previous crops can reduce weed problems in


Plant roots grow in the presence of water,

not in search of it.

alfalfa. The topic of weed control in a new alfalfa seed-ing is covered at length in chapter 6.

C O M PA N I O N C RO P S

Small grains, primarily oats, are sometimes plantedwith alfalfa as a companion crop (also called a nursecrop). The proported benefits of a companion crop areweed control, increased forage yields the first cuttingof the seeding year, and wind and frost protection fortender alfalfa seedlings. However, the risk associatedwith companion crops is excessive plant competition,which can reduce alfalfa stand, vigor, and yield of sub-sequent alfalfa cuttings. Trials conducted several yearsago in Butte Valley demonstrated that competitionfrom a companion crop reduced alfalfa seedling rootlength by 3 to 4 inches. Alfalfa seedings are oftenstressed for lack of water during harvest of the com-panion crop. This reduces root growth and possiblythe future productivity of the alfalfa stand.

The advisability of planting an oat companion cropdepends on several factors, including planting date ofthe alfalfa, oat seeding rate, weed species present andtheir population level, cost of weed control, expectedseverity of wind or frost, and the hay market. If a com-panion crop is used, the key to success is managing thefield to the advantage of the alfalfa rather than thecompanion crop. Oat seeding rates should not exceed20 pounds per acre or excessive competition willoccur. The field should be cut based on the maturity ofthe alfalfa and not the oats. However, if the compan-ion crop is overtopping alfalfa seedlings and restrictinglight penetration, cut the field early; this will allowmore sunlight to reach the alfalfa seedlings. The great-est damage from companion crops generally occurswhen the grain crop lodges, or falls. Therefore, managethe field to avoid lodging: use a low oat-seeding rate,

apply little or no nitrogen fertilizer, and choose shortoat varieties that are not prone to lodging.

Cereals other than oats have been used as compan-ion crops. Many newer varieties of wheat and barleyhave very large leaves that can cut off light to alfalfaseedlings. These varieties, therefore, are undesirablecompanion crops.

The best advice to most growers is, Do not use acompanion crop. However, for cases where a compan-ion crop is needed—where soil crusting is a problemor where blowing sand can cut off young seedlings, donot exceed a seeding rate of 20 pounds per acre. Insuch cases, minimize competition from the compan-ion crop by seeding the cereal on a 12-inch row spac-ing perpendicular to prevailing winds. (The normalspacing would be 6 to 7 inches.) Another alternative isto use an herbicide such as Poast to control the com-panion crop when it is young, before it competes withthe alfalfa. Whether a companion crop is used or not,remember that the primary goal when seeding alfalfa isto establish a long-lived productive stand of alfalfa.The short-term benefits of a companion crop can benullified if the alfalfa stand and vigor suffer fromexcessive competition.

S E E D I N O C U L AT I O N

Nitrogen-fixing Rhizobium bacteria, which are foundin alfalfa root nodules, usually supply the plant withnitrogen needed for growth. Existing populations of nitrogen-fixing bacteria ordinarily provide adequatenodulation in fields with a history of alfalfa produc-tion. However, there are rare fields with a history ofalfalfa production that benefit from seed inoculation.

Inoculate soils without a recent history of alfalfaproduction. Commercial inoculum is available forseed treatment. Be sure to use fresh inoculant and donot expose it to hot, dry conditons prior to planting. Ifyou are unsure of the history of a field, inoculum ischeap insurance.

F U N G I C I D A L S E E D C OAT I N G S

There are years and field situations in which fungicide-treated seed would reduce stand loss during establish-ment, but these cases are believed to be rare. Seedlingdiseases are uncommon in the Intermountain Region.


Benefits of a companion cropcan be nullified if alfalfa

stand and vigor suffer fromexcessive competition.

At a given seeding rate in pounds per acre, approximate-ly one-third fewer seeds are planted if the seeds are coat-ed, due to the weight of the coating. Unless seedlingdiseases are known to be a problem, plant raw seed.

T I M I N G O F T H E F I R S T H A RV E S T

The last step in alfalfa stand establishment is decidingwhen to make the first cutting. Carbohydrates pro-duced during photosynthesis are stored in roots.Stored carbohydrates provide the energy for regrowthafter cutting. Premature cutting does not allowsufficient time for root reserves to accumulate, so itreduces alfalfa vigor and possibly the yield of subse-quent cuttings. Alfalfa should be “established” prior tothe first cutting. The appearance of bloom has beenused as an indicator of whether the stand is estab-lished, but several factors can cause alfalfa to bloomprematurely. The number of stems per plant is a farbetter indicator of when to cut. Do not cut seedlingalfalfa until it has developed at least three stems(Figure 2.4). Some experts recommend that the rootsof alfalfa grown in sandy or sandy loam soil be at least

14 inches deep prior to the first harvest. Such roots aredeep enough to avoid impedance from traffic-inducedcompaction layers. If you are forced to cut alfalfa pre-maturely, whether to remove weeds or for any otherreason, lengthen the interval between the first and sec-ond cuttings. This will allow the young alfalfa plantssufficient time to recover and replenish depleted rootreserves.


Frate, C., S. Mueller, and R. Vargas. 1992. Central San JoaquinValley alfalfa establishment and production. Fresno, CA:University of California Cooperative Extension.

Tesar, M. B., and V. L. Marble. 1988. Alfalfa establishment. In A.A. Hanson, D. K. Barnes, and R. R. Hill, Jr. (eds.), Alfalfa andalfalfa improvement, 303–32. Madison, WI: American Societyof Agronomy, Crop Science Society of America, and SoilScience Society of America. Number 29.

Undersander, D., N. Martin, D. Cosgrove, K. Kelling, M.Schmitt, J. Wedberg, R. Becker, C. Grau, and J. Doll. 1991.Alfalfa management guide. Madison, WI: American Society ofAgronomy, Crop Science Society of America, and Soil ScienceSociety of America.


19

C H A P T E R T H R E E

VA R I E T Y

S E L E C T I O NHarry L. Carlson

�lfalfa growers in the IntermountainRegion, like growers elsewhere,need to select alfalfa varieties based

on yield and quality performance in their specificregion. The varieties best suited for the high-elevationintermountain valleys of northeastern California aredifferent from the varieties adapted to the warmer,longer-season production areas in the remainder ofthe state.

After choosing varieties with growth characteristicsand pest and disease resistances suitable for your area,plant test strips to check their performance underspecific field and management conditions. Time andmoney spent on selecting the most suitable varietywill be rewarded with higher yields and a net increasein profits.

Y I E L D

Economics force growers to be concerned about theyield potential of selected varieties. Many costs associ-ated with crop production are fixed costs, such as thoserelating to stand establishment, land rent or owner-ship, and equipment ownership. The increased yieldafforded by the selection of an improved varietyspreads these costs over greater amounts of hay, whichlowers the cost of production per ton of hay produced.

Restated, it simply costs less per ton to produce high-yielding alfalfa, particularly if the increased yields arethe result of a simple change to an improved variety.

S TA N D P E R S I S T E N C E

Annual yields are important, but it is the yield of thecrop over the total years of production, or life of thestand, that determines the actual profitability of thecrop. The cost of alfalfa stand establishment is rela-tively fixed for a given farm operation. The effect ofstand establishment costs on overall profitabilitydepends largely on the number of years that the cropis in production. The longer the stand life, the greaterthe number of years in which to recover the cost ofestablishment. Generally, growers in the Intermoun-tain Region would like to maintain stands for 5 yearsor more, with a stand life of 7 years being typical.Failure to meet this goal means that establishmentcosts will be spread over fewer growing seasons; thetotal cost of production per year will be higher.

Harvesting alfalfa in variety trial, Tulelake, California.

Stand life refers to the need to maintain minimumaverage plant populations greater than five or sixplants per square foot. Fields with stands below thislevel will have reduced yields (see chapter 15). Also,sparse stands usually produce thick-stemmed, “low-test” hay that may be quite weedy. With the highcost of producing and making hay, growers cannotafford to farm fields when poor stands result in lowyields or low-quality hay.

The most important varietal factor in maintainingadequate stands in the Intermountain Region is win-ter hardiness. The intermountain area is subjected tomonths of subfreezing winter temperatures. To makethings worse, these cold temperatures often occurwithout the benefit of an insulating blanket of snow.Accordingly, varieties without winter hardiness sufferwinterkill and stands may be reduced to subeconomiclevels after only one or two seasons. Of course, plantpopulations can be reduced by other factors, such asdisease or cultural mismanagement; but if a variety isnot sufficiently winter hardy, optimum managementof other production factors will not prevent winterstand loss.

FA L L D O R M A N C Y

A major component of winter hardiness is fall dor-mancy. Dormancy refers to a variety’s tendency to ceasegrowth in the fall as days shorten and temperaturesdrop. Dormant varieties begin growing again in thespring as soil temperatures warm. The fall dormancyof a variety can be classified based on industry stan-dards for fall regrowth. On this scale, the dormantvariety Vernal is rated as a 2, less dormant varietiessimilar to Ranger receive the rating of 3, and semidor-mant varieties similar to Saranac are grouped in class 4(Table 3.1 and Figure 3.1).

Plants that are winter dormant are much less sus-ceptible to cold temperatures and winterkill (Figure3.2). Less-dormant varieties that begin growth early inthe spring may be hit by early spring frosts that candamage both yield and quality of the first cutting(Figure 3.3; see color photo 3.1). In contrast, the yieldof third or fourth alfalfa cuttings may be reduced indormant varieties that go dormant early in the fall.

Thus, the selection of a variety with the proper dor-mancy is a compromise. Select varieties that aresufficiently dormant to assure winter survival and to

prevent premature spring growth, but do not selectthose varieties that are so dormant that valuable grow-ing days are lost in spring and fall. In studies conduct-ed in Tulelake, California, the varieties that producedthe highest yields with adequate winter survival tend-ed to be in fall dormancy class 3 (Figure 3.4). In inter-mountain areas with warmer, longer growing seasons,dormancy class 4 varieties may be better performers.Dormancy class 2 varieties would perform better in


15

5

0

25

20

10

Variety and Dormancy Rating

Fall

Regr

owth

(inc

hes)

Spredor(1)

Vernal(2)

Ranger(3)

Sarnac(4)

Lahontan(6)

Figure 3.1. Observed fall regrowth of standard varieties for fall dor-mancy rankings. (Data were gathered in a 1986 variety trial,Tulelake, California.)

Figure 3.2. Fall dormant varieties are less susceptible to stand lossfrom winterkill. (Data were gathered in fifth-year stands in a varietytrial planted in 1981, Tulelake, California.)

Figure 3.3. Spring frost injury is more likely with less-dormant vari-eties. (Data were gathered in a 1985 variety trial, Tulelake,California.)

6

5

4

3

Dormancy Rating

Stan

d (p

lant

s/sq

. ft.)

1 2 3 4 5 6 7

40

30

20

50

Dormancy Rating

Sprin

g Fr

ost I

njur

y (%

)

1 2 3 4 5 76

v a r i e t y s e l e c t i o n 21

intermountain areas with seasons that are cooler andshorter than those typical of the Tulelake region.These distinctions are not absolute. Growers shouldconsider varieties with dormancy ratings one aboveand one below the rating generally recommended foryour region.

P E S T A N D D I S E A S E R E S I S TA N C E

The yield performance and stand life of an alfalfa vari-ety are assumed to be related to the pest and diseaseresistance of the cultivar. Cultivar resistance may be

less important in the Intermountain Region than inother areas, however. Many areas in the Intermoun-tain Region are not plagued by several of the seriousdisease and pest problems that significantly limit alfal-fa production in other regions. A variety with littlepest or disease resistance may perform very well there.This does not mean that pest and disease resistance arenot important—it only indicates that a review of yieldresults from one area may not show the whole picture.

In specific fields, varietal pest and disease resistancemay be critical. For example, high resistance toPhytophthora root rot may not be needed in the verywell drained soils common in areas such as Tulelake,

Table 3.1. Alfalfa varieties categorized by fall dormancy class, whichare based on fall growth.

FA L L S TA N D A R D E X A M P L ED O R M A N C Y C L A S S VA R I E T Y VA R I E T I E S

1 (very dormant) Norseman Spredor 3

2 (dormant I) Vernal DK 122,

Avalanche +Z

3 (dormant II) Ranger Blazer XL,

Centurion

4 (moderately dormant I) Saranac Agressor,

Webfoot MPR

5 (moderately dormant II) DuPuits Archer, Robust

6 (semidormant) Lahontan

7 (moderately nondormant) Mesilla

8 (nondormant) Moapa 69

9 (very nondormant) CUF 101

Table 3.2. General guidelines for varietal pest and disease resistanceneeded in the Intermountain Region.

P E S T O R D I S E A S E R E S I S TA N C E C L A S S

Bacterial wilt Resistance (R)

Verticillium wilt Resistance (R)

Fusarium wilt High resistance (HR)

Southern anthracnose Resistance (R)

Phytophthora root rot Resistance (R)

Spotted alfalfa aphid Susceptible (S)

Pea aphid Resistance (R)

Blue alfalfa aphid Moderate resistance (MR)

Stem nematode Resistance (R)

Root-knot nematode Resistance (R)

Figure 3.4. In Tulelake, California, varieties with a dormancy ranking of 3 provide the best average yield performance. Some varieties in dor-mancy rankings 2 and 4 perform well also. (Data reflect 6-year average yields from 45 varieties, 1981–86.)

Varieties Grouped by Dormancy Rating2 3 4 5 6

Yiel

d (to

n/A)

6.5

5.5

6

5

VE

RT

ICIL

LIU

M W

ILT


FAL

L D

OR

MA

NC

Y*

AN

TH

RA

CN

OSE

RA

CE

1

PH

YT

OP

HT

HO

RA

RO

OT

RO

T

SPO

TT

ED

AL

FAL

FA A

PH

IDP

EA

AP

HID

BLU

E A

LFA

LFA

AP

HID

STE

M N

EM

ATO

DE

NO

RT

HE

RN

RO

OT

-

KN

OT

NE

MAT

OD

E

FUSA

RIU

M W

ILT

BA

CT

ER

IAL

WIL

T

Table 3.3 Fall dormancy and pest resistance ratings for alfalfa varieties

PEST RESISTANCE * *

Spredor 3 1 HR MR HR R MR S MR — MR —

5262 2 HR LR MR — R R R — MR —

Agate 2 HR — HR MR R — — — — —

Alfagraze 2 MR — R MR LR — R — R —

Avalanche + Z 2 HR HR HR HR HR — R — MR —

DK122 2 HR R R HR HR MR R — — —

Pacesetter 2 HR R R HR HR — — — — —

Sterling 2 HR R HR HR HR R R — — —

Vernal 2 R — MR — — — — — — MR

WL 252 HQ 2 HR R HR HR HR MR R LR R —

120 3 HR — LR LR R — R — — —

5246 3 HR R HR HR HR R R — MR —

5396 3 R R R HR R R R — HR MR

Achieva 3 R R HR HR HR R R — MR —

Arrow 3 HR R HR MR HR — R — MR —

Blazer XL 3 R R HR HR HR HR R — R —

Centurion 3 HR R R R R MR R — — —

Class 3 HR R R HR HR R R — MR —

Columbo 3 R HR HR R R R HR — MR MR

Guardian 3 HR HR HR HR HR — HR — R R

Innovato+Z 3 HR HR HR HR HR MR R S R —

MultiKing 1 3 HR R HR R R MR MR — MR —

Oneida VR 3 R HR HR MR MR — — — — —

Treasure 3 HR R HR HR R MR R — MR —

Ultra 3 R R HR HR R LR R — R —

Victory 3 HR R HR HR MR — — — — —

Webfoot 3 R — MR — R — — — — —

5364 4 R MR R MR MR HR HR — R —

5472 4 HR MR HR MR MR R HR — R —

Affinity +Z 4 HR HR HR HR HR — R — R —

Agressor 4 HR R HR HR HR MR HR MR MR —

Allstar 4 HR R HR HR HR LR R — R MR

Apollo Supreme 4 HR R HR HR R — HR — — —

Aspen 4 HR R HR HR HR — HR — R R

Cimarron VR 4 HR R HR HR R HR HR MR R —

Crystal 4 HR R HR R HR LR R MR MR —

DK133 4 HR R HR HR HR R R — MR —

Extend 4 HR R R HR HR — HR — R —

Fortress 4 R R R — HR HR R — HR —

Laser 4 HR R HR R HR MR — MR — MR

Magnum III 4 R MR R MR R MR R MR MR —

MagnumIV 4 HR R HR R HR MR — MR R MR

Webfoot MPR 4 HR HR HR HR HR — R — — —

WL 322 HQ 4 HR R HR MR R HR HR R LR LR

WL 323 4 HR R HR HR HR MR R — HR —

Archer 5 MR MR HR R R HR HR R R R

Robust 5 R R HR R R R R MR R MR

Lahontan 6 MR — LR — LR MR LR — R —

*FallDormancy Ratings

1 = Very dor-mant2 = DormantI3 = DormantII4 =Moderately

dormantI5 =Moderately

dormantII6 =Semidormant

** Pest-Resistance

RatingsS =SusceptibleLR = Low

Resistance MR =ModerateResistanceR =Resistance HR = HighResistance

Source:Associationof Official

but high resistance to this disease is clearly required inwet, poorly drained fields in other intermountain pro-duction areas. Likewise, stem nematode resistance maynot be important in the region as a whole, but it is crit-ical in fields that have stem nematode infestations.

Although the minimum resistance levels requiredwill vary for different fields and production areas, theguidelines in Table 3.2 are helpful when consideringresistance needs for a field about which little is known.As more is learned about the problems in a specificfield or area, the grower can select varieties with moreor less resistance than suggested; the important thingis to counter a problem with a variety with resistanceto it. Pest and disease resistances that may be critical inspecific fields include resistance to bacterial wilt,Phytophthora root rot, Fusarium wilt, anthracnose,pea aphid, stem nematode, and root knot nematode.

The serious crop-threatening disease Verticilliumwilt has recently been identified in a few isolated fieldsin the Intermountain Region. Because of the potentialseriousness of Verticillium wilt, intermountain pro-ducers may wish to select varieties with resistance tothis disease.

For information on relative resistance of varieties,refer to Table 3.3 or obtain a current copy of FallDormancy and Pest Resistance Ratings for AlfalfaVarieties produced by the Certified Seed Council(Davis, California). Note that resistance in a variety isnot absolute. Alfalfa varieties have diverse geneticbackgrounds, so a portion of the plants of resistant oreven highly resistant varieties may be susceptible tothe rated pest or disease. Table 9.1 (chapter 9) explainsthe resistance rating system and describes the percent-age of resistant plants in each rating category.

H AY Q U A L I T Y

Quality is critical to the sale price of alfalfa hay.Growers need to match the quality of the hay pro-duced with the demands of the market in which theychoose to sell. For example, dairy hay demands a pre-mium price but must also meet exacting quality teststandards. Ideally, growers should select varieties tomeet such criteria. Unfortunately, it is not that simple.Many factors other than variety selection affect hayquality. Factors such as stand density and cuttingschedule have a great effect on quality. As mentioned,hay quality will decline as plant stands thin. Generally,

alfalfa cut at an early stage of maturity is of higherquality than more mature alfalfa (see chapter 11).Management of irrigation, fertilizer, weeds, insects,and disease can have major impacts on hay quality.Because of the confounding effects of all these factors,measuring small differences in quality among differ-ent varieties is extremely difficult. One variety mayproduce the highest-quality hay under one set of con-ditions, but it may not perform as well as other vari-eties when grown under different management.

This is not to say that quality differences amongvarieties do not exist—only that such differences aregenerally small and difficult to measure. Accordingly,very little unbiased information is currently availableto help growers distinguish one variety from anotheron the basis of quality. Improved hay quality is a majoremphasis in the current breeding programs of majoralfalfa seed companies, and new varieties with measur-able improvement in quality characteristics may beforthcoming in the near future. For now, the best avail-able recommendations in regard to quality are to main-tain healthy plant stands and to match the cultural andcutting management of a field to the growth character-istics of the variety selected (see chapter 11).

S O U RC E S O F I N F O R M AT I O N

This chapter has already mentioned the informationavailable from the Certified Alfalfa Seed Council. Inaddition, seed company representatives are a readysource of information about specific alfalfa varieties.Do not hesitate to ask pointed questions about varietydormancy groups, pest and disease ratings, and rela-tive yield and quality performance in your area. TheUniversity of California (UC) is another source of

v a r i e t y s e l e c t i o n 23

Never use yield results from a single cutting or

even a single year to make a variety selection

information. For years UC has conducted large alfalfavariety trials at the Intermountain Research andExtension Center in Tulelake, and UC Farm Advisorshave conducted many variety tests in the major alfalfa-producing valleys throughout the intermountain area.Farm Advisors can provide growers and seed handlerswith the performance results from these studies.

I N T E R P R E T I N G Y I E L D T R I A L R E S U LT S

Performance information can be gleaned from reportsof university-conducted research, provided that thetests were conducted under representative climaticconditions and management. Remember, the closerthe test was to home, the greater the likelihood thatresearch information will apply to a specific set of localconditions. Also, where possible, select varieties thathave been in trials for multiple years at more than onelocation. A variety will be exposed to a range of cuttingand weather conditions in different fields and over thelife of the stand. The greater the number of years andlocations tested, the greater the likelihood that the testdata will reflect the various conditions a variety mayencounter. Never use yield results from a single cuttingor even a single year to make a variety selection.

In reviewing test results, avoid the temptation toautomatically select the top-yielding variety. Typically,varieties yielding near the top of a given trial have mea-sured yields only a small fraction of a ton less thanthose of the top-yielding variety. Such small differ-ences may be the result of very small errors in theexperimental technique. It is prudent to look at all thevarieties in the top-yielding group and make final vari-ety selections based upon factors in addition to yield.Such factors include relative pest and disease resis-tance, quality, experience with or information aboutthe varieties, and seed price.

Once a new variety is selected, consider plantingsmall test strips, 1 to 5 acres in size, of the new varietyto check performance under your specific field andmanagement conditions. Do not plant test strips onthe edge of a field or in isolated or poor areas of thefield. In a fair test the new variety receives manage-ment typical for the field. Count bales from the teststrips to estimate yield and collect separate samplesfrom the bales to determine quality.

VA R I E T I E S ,B R A N D S , A N D B L E N D S

This chapter refers primarily to alfalfa varieties recog-nized by the Association of Official Seed CertifyingAgencies. Alfalfa seed can also be purchased as tradename brands or as blends of various brands and vari-eties. Like recognized varieties, some blends and brandsperform well and some perform poorly. The dilemmain dealing with blends and brands is that you cannot besure that the material tested and discussed in reports ofexperimental trials is the same as will be sold under thatspecific name in the future. The varieties that make upa blend often vary from year to year, depending on seedavailability. When you purchase a blend or brandbecause you used it successfully in the past, make surethat what you buy actually has the same components asthe combination you bought before.

S E E D P R I C E

Paying extra money for seed of a variety that does notoutperform seed of a less expensive cultivar is certainlyfoolish. On the other hand, it takes only a small differ-ence in yield or stand life to justify a large difference inseed cost. For example, a grower who pays an extradollar per pound for seed of a new variety that pro-vides as little as a 5 percent improvement in yield(about 0.33 ton per acre per year, for a 6-year period)is money ahead. At planting the seed costs an extra$20 per acre, but over the life of the stand it providesan average increase in net profits of $200 per acre. As arule, money used to purchase high-quality, certifiedseed of a locally adapted variety is money well spent.


Certified Alfalfa Seed Council. 1994. Fall dormancy and pest resis-tance ratings for alfalfa varieties. Davis, CA: 1994/95 edition.

Hill, R. R., Jr., J. S. Shenk, and R. F. Barnes. 1988. Breeding foryield and quality. In A. A. Hanson, D. K. Barnes, and R. R.Hill, Jr. (eds.), Alfalfa and alfalfa improvement, 809–25.Madison, WI: American Society of Agronomy, Crop ScienceSociety of America, and Soil Science Society of America.Number 29.


25

C H A P T E R F O U R

I R R I G AT I O NSteve B. Orloff, Harry L. Carlson, and Blaine R. Hanson

�he Intermountain Region has a high-desertclimate where irrigation must provide themajority of water needed for alfalfa

growth. Improper irrigation management limits alfal-fa yields in the Intermountain Region more often andto a greater extent than does any other aspect of alfalfaproduction. The return from other inputs (i.e., varietyimprovement, fertilizer, and pest control) will besignificantly reduced or eliminated if a lack of waterlimits crop development. Therefore, properly appliedand timed irrigations are critical for maximum yieldand profit.

Figure 4.1 shows the typical alfalfa yield response to applied irrigation in the Intermountain Region. Asirrigation increases, so do alfalfa yields—but only to the point where crop water needs have been met.Applying water over and above crop requirements doesnot improve yield and only adds to the cost of produc-tion. What is more, excess water may increase pest anddisease problems and shorten alfalfa stand life.

The actual shape of the yield response curve variesfrom location to location and from year to year. Theminimum yield without irrigation, the optimum irri-gation level, and the maximum potential yield varybased on soil type, rainfall, and seasonal temperatures.Still, most alfalfa grown in the region follows the trendillustrated in Figure 4.1.

Proper irrigation management leads to increasedyields, improved stand health, and a reduction inunnecessary water use. This chapter will discuss thebasics of alfalfa irrigation scheduling and water appli-

cation techniques. Sound irrigation practices are basedon an understanding of how water is stored in the soil,crop water requirements, and irrigation system designand operation.

WAT E R S TO R A G E

Soil is the storage reservoir from which plants extractwater (Figure 4.2). If too much water is applied, thestorage reservoir will overflow and water will run offor percolate below the root zone of the crop. If thestorage reservoir gets too low, plants will be stressedand yield reduced. The key to irrigation managementis to keep the soil-water reservoir full enough to avoidplant stress but not overfill the reservoir.

Soil type determines the capacity of the soil reser-voir. Soil is composed of soil particles of varying sizes,

organic matter, and voids, or pore spaces. Water occu-pies some of the pore spaces and is held as a filmaround soil particles. The more pore spaces, thegreater the water-holding capacity. Sandy soils (coarse-textured soils) have large pores, but fewer total poresthan clay (fine-textured) soils. Therefore, the water-holding capacity of sandy soils is far less than that ofclay soils.

Available Water

After an irrigation or heavy rainfall, water fills the porespaces; the soil is saturated. Under the influence ofgravity, water drains from the larger pore spaces andgradually moves deeper into the soil profile. Downwardmovement of water slows considerably within 1 to 3

days after irrigation. The water that remains in the soilafter this initial drainage is considered stored. Whenthe soil has stored all the water it is capable of holding,the soil profile is full, or at field capacity.

Not all the water held in soil is available to plants. Aportion is held so tightly by soil particles that it isunavailable. The amount of water plants can extractfrom the soil is called available water. If plants extractall the available water, the soil dries to the permanentwilting point. When this happens, plants wilt and die.Table 4.1 shows the available water content for differ-ent soil types. Note that the available water content ofcoarse sand is very small (less than 1 inch availablewater per foot of soil) compared to that of the claysoils (which have more than 2 inches available waterper foot of soil). Table 4.1 cites values for general soiltypes. To find values for your soils consult Soil Surveysavailable from the Natural Resources ConservationService, or study University of California (UC) Leaflet21463, Water-Holding Characteristics of CaliforniaSoils.

Water Storage Capacity

To determine the total water storage capacity of a soil,a grower must consider the rooting depth of the crop.Although alfalfa roots may penetrate as deep as 12 feetin some soils, the effective rooting depth for irrigationpurposes is generally assumed to be 4 feet. Theassumption is based on the fact that most of the wateris extracted from the upper portion of the root system(Figure 4.3). Approximately 70 percent of the water isextracted by the upper half of the root system. To cal-culate the total storage capacity of the soil, multiplythe available water content of the soil in inches perfoot of soil by the rooting depth of the crop. Forexample, the calculation to determine the availablewater storage capacity of a sandy loam soil follows.

1.5 in. available water/ft.x 4 ft. of rooting depth

6 in. total storage capacity

If you are calculating the water storage capacity of afield of young alfalfa or a field with a restricted rootzone, dig a hole to see how deep the roots actually go.If you used the standard 4-foot rooting depth in yourcalculation, the result will be inaccurate.


10.00

9.00

7.00

5.00

4.00

3.00

2.00

1.00

0.00

8.00

6.00

Applied Irrigation (acre inches per season)

Fora

ge Y

ield

(ton

s/ac

re)

0 5 10 15 20 25 30

Figure 4.1. Typical yield response of alfalfa to applied irrigation inthe Intermountain Region.

Figure 4.2. Think of the soil-water reservoir as a storage tank. Onlya portion of the water in the tank is available to plants. To avoidyield reductions, keep the storage tank filled to a level between fieldcapacity and the allowable soil depletion level.

Field capacity

Permanent wilting point

Allowable depletion

Unavailable water

Available water

Allowable Depletion

As soil dries, soil particles hold stored water moretightly. Extracting water becomes increasingly difficultfor plants. Extraction may become so difficult thatplants cannot meet their water needs. If this occurs,growth slows and yields decline. The amount of waterloss that can occur before water extraction becomestoo difficult is termed the allowable depletion (Table4.1). For alfalfa, allowable depletion is 50 percent. Toavoid yield reductions, irrigate the field before 50 per-cent of the available water has been depleted. Keep inmind, however, that 50 percent allowable depletion isa maximum value. Fields can be irrigated before 50percent of the available water has been depleted with-out reducing yield.

As you can see, an understanding of soil propertiesallows you to answer the two questions paramount toirrigation: When to irrigate? and How much to apply?Irrigate the field when 50 percent or less of the avail-able water in the soil has been depleted. The amountof water to apply is the amount required to fill the soilreservoir to field capacity.

I R R I G AT I O N S C H E D U L I N G

Two principle methods are used to schedule irriga-tions in alfalfa fields. One method relies on soil-basedmeasurements; the other is called the water budgetmethod; and it involves weather monitoring. Bothmethods can be equally effective. The best approach,however, is to use both. Throughout the season, verifyrecommendations based on the water budget methodby using soil-based measurements.

The Soil Moisture Method

Measuring soil moistureThe moisture status of soil can be monitored in variousways. Each of the moisture measurement techniquesdescribed below can help to schedule irrigations.

t h e l o o k - a n d - f e e l m e t h o d Enoughexperience with a given soil type allows a grower toestimate soil moisture conditions by simply feelingthe texture and dampness of a soil sample. For exam-ple, samples from clay or clay-loam soils that can bemade into a firm round ball with light hand pressure

i r r i g a t i o n 27

Figure 4.3. Typical water extraction pattern of alfalfa roots.

40%

Percent of total water extracted

30%

20%

10%

Table 4.1. Estimates of available water content and allowable depletion for different soil types.

4 F T RO OT ZO N E 1

AVA I L A B L E A L L OWA B L E AVA I L A B L E A L L OWA B L E WAT E R D E P L E T I O N WAT E R D E P L E T I O N

S O I L T Y P E ( I N . / F T. ) ( I N . / F T. ) ( I N . ) ( I N . )

Coarse sand 0.5 0.25 2.0 1.0

Fine sand, loamy sand 1.0 0.50 4.0 2.0

Sandy loam 1.5 0.75 6.0 3.0

Fine sandy loam, loam, silt loam 2.0 1.00 8.0 4.0

Clay-loam, silty clay 2.2 1.10 8.8 4.4

Clay 2.3 1.15 9.2 4.6

Organic clay loams 4.0 2.00 16.0 8.0

1. A 4-foot root zone is a typical effective rooting depth for alfalfa.

are considered to be adequately moist, but samplesthat crumble into powder when crushed in hand areconsidered to be too dry. The look-and-feel methodworks well for many experienced growers, but it isfairly imprecise. Its major disadvantages are thatproper feel and texture vary among soil types and theability to schedule irrigations based on feel alonerequires skill and years of experience. The majoradvantages of this method are that it is quick andsamples can be easily taken from many areas of thefield. The ability to check fields often is importantbecause the look-and-feel method does not indicatewhen the soil is becoming too dry. In other words,some water stress might occur before the look-and-feel method indicated the need to irrigate.

t e n s i o m e t e r s Soil moisture tensiometers mea-sure how strongly soil particles hold water. Wet soilholds water more loosely than dry soil.

A tensiometer is usually a 1-inch tube made of plastic. It is filled with water and sealed on the top witha mounted vacuum gauge. On the bottom, the tube isfitted with a porous ceramic tip. The tube is installed insoil, with the tip at the desired monitoring depth. Assoil dries, water moves out of the tube, through theporous tip, and into the drying soil. The movementout of the tube creates a suction (negative pressure)that the gauge measures. The drier the soil, the greaterthe negative pressure measured on the gauge.

Researchers have determined the allowable soil de-pletion, in terms of tensiometer pressure readings, formany crops. Yield loss does not occur with alfalfa untilnegative pressures rise above 70 to 80 centibars—thepressure depends on the soil type. Plant stress occursat lower tension readings in sandy soil than in heavyclay soil.

Reading a tensiometer is quick and convenient. By

placing several tensiometers at different depths, youcan quickly determine soil moistures at various loca-tions in the root zone. The major advantage of ten-siometers is that pressure readings can be correlatedwith plant yield responses.

The biggest disadvantage of tensiometers is that theyneed to be permanently installed. In some installationsthe gauge and top portion of the tensiometer is aboveground. This makes haying difficult and haying equip-ment often damages the meters. However, more elabo-rate installations can be made that place the wholeinstrument below ground. Frequent replacement isexpensive because of the cost of parts and labor.

Tensiometers must be properly installed to workcorrectly. Take extra care to seat the instrument’s tipinto the soil and to avoid gaps between the tube andsoil that allow irrigation water to run down the sideof the tube. Tensiometers also require frequent servic-ing to replace the water lost from the tube. Theymust be removed in the winter to prevent damagefrom freezing.

m o i s t u r e b l o c k s Although many models ofmoisture blocks are available, they all do the samething. They electronically monitor the relative mois-ture content of a buried ceramic or gypsum block. Asthe soil dries, the relative moisture content of theburied block also declines. Some models measure themoisture content of the buried block by measuringthe resistance between internal electrodes in theblock; others measure heat dissipation between a heatsource and a thermistor. Regardless of how the blockworks, meters are available that read in centibars, andthe readings are approximately equivalent to thosefrom a tensiometer: Allowable depletion occursbetween 70 and 80 centibars, depending on soil type.

Like tensiometers, moisture blocks are easy to readat any time. They can be installed at several depths ata given monitoring site, and the readings correlatewell with plant moisture needs. In addition, theblocks may be fitted with long underground wiresthat lead to a central reading station. Such aconfiguration greatly minimizes the risk of equip-ment damage to the block, and it certainly makesreading the blocks more convenient.

Disadvantages of the blocks are the high purchasecost, the care and time needed to install the blocks inthe soil, and the problem of tearing out wire leads ifthe wires are not set underground or if reading sta-


Improper irrigation . . . limits alfalfa yields . . . moreoften and to a greater extent

than any other aspect of alfalfa production.

tions are not well placed. With moisture-sensitivecrops such as many vegetables, soil moisture blockshave the additional disadvantage of not being as sensi-tive as tensiometers under high soil moisture condi-tions. Fortunately, deep rooted alfalfa can toleratelower soil moisture readings so the drier operationalrange of moisture blocks is adequate for irrigationscheduling in alfalfa.

n e u t r o n p r o b e s The most technologicallyadvanced method of measuring soil-water content isthe neutron probe. This instrument contains aradioactive source and measures soil-water contentby emitting fast neutrons into the soil and then mea-suring the return of slow neutrons back to the instru-ment. The number of neutrons returned is directlyproportional to the number of hydrogen atoms theinitial emission encountered. Most of the hydrogenatoms in the soil are components of water, so thenumber of returning neutrons reflects water content.

Because of cost, technical complexity, and healthand safety regulations regarding the use of radioactivematerial, leave neutron probes to professional irriga-tion consultants who have the training and permitsrequired to use the instrument.

Using soil moisture dataThe best way to apply soil-moisture measurements toirrigation scheduling is to plot the measurements on agraph. The plotted data present a picture of how fastthe soil is drying (Figure 4.4). For example, followinga full irrigation that completely fills the soil profile,the tensiometer reading is low (point A in Figure 4.4).As alfalfa grows, it draws on the soil-water and thetensiometer readings begin to rise. After a few pointshave been plotted, you can estimate approximatelyhow many days it will take for the soil to dry to theallowable depletion (80 centibars in this example). Byday 10, in this example, three points have been plot-ted, so you can estimate that the soil will be dryenough to warrant irrigation on about day 20. Thenext reading, on day 14, confirms this estimate; wateris applied on day 20. By that time the soil had indeeddried to the point of allowable depletion and irriga-tion was necessary. The graph indicates that the irriga-tion did not completely refill the soil profile—that is,on the day following irrigation, the tensiometerdropped to only about 40 centibars (point C). As

explained earlier, the amount of water to apply in agiven irrigation is determined by the soil type and thepercentage depletion. The soil in this example is a finesandy loam, so the allowable depletion is about 4 inch-es (1 in. x 4 ft of rooting depth). The irrigation appliedat point B was less than 4 inches, so another irrigationwas needed 10 days later. The second irrigation was a4-inch irrigation, which filled the soil profile andreturned the tensiometer reading to near 0 (point D).

In scheduling irrigations or in monitoring irriga-tion effectiveness, it is important to sample soil mois-ture at more than one depth. In the case of a maturealfalfa crop, place tensiometers or moisture blocks at18 inches and 36 inches in the soil. Use readings takenat 18 inches to schedule irrigations; use the readings at36 inches to determine if the crop is using deep waterand if irrigations are completely filling the soil profile.

The Water Budget Method

u n d e r s ta n d i n g t h e wat e r b u d g e t

c o n c e p t As the term budget implies, the waterbudget method involves tracking additions and losses


100

90

70

50

40

30

20

10

0

80

60

Days

Tens

iom

eter

Rea

ding

(cen

tibar

s)

0 10 20 30 40 50 60

A

B

C

D

Figure 4.4. Plot of tensiometer readings following irrigation anddrying cycles. A = initial low tensiometer reading following a fullirrigation; B = reading indicating high pressure following severaldays of crop water use, just prior to an irrigation; C = reading afterpartial irrigation that did not fill the soil profile; D = reading after afull irrigation.

and balancing them. The losses are due to crop wateruse and inefficiencies in the irrigation system. Theadditions are due to irrigation and rainfall. The objec-tive of the water budget method is to maintain soilmoisture near the optimum level by keeping track ofcrop water use and then irrigating to replace the waterused. Knowledge of crop water use is essential to usingthe water budget approach.

Crop water use is also called evapotranspiration(ET). The term evapotranspiration refers to the com-bined loss of water through evaporation from the soiland from water taken up and evaporated from theplant (transpiration). The rate at which plants usewater is determined by the growth stage of the plantand by weather. Small plants use less water than largeplants, for example, and all plants use more waterwhen it is hot than when it is cool. Plants use morewater on sunny days than cloudy days, and on dayswith high winds. For these reasons, plants use muchless water in the spring and fall than during the longhot days in the middle of the summer. Figure 4.5

shows how daily water use of alfalfa near Tulelake,California, fluctuates throughout the growing season.

Over the years, irrigation scientists have quantifiedthe effects of weather on plant water use. By usingweather data you can predict with reasonable accuracythe water use of alfalfa in a specific region. The dataneeded include measurements of relative humidity,wind velocity, air temperature, and light intensity.Irrigation science has progressed to a point where suchpredictions are sufficiently accurate to be used for irri-gation scheduling.

Crop water use values for irrigation scheduling maybe obtained from several sources. Some local newspa-pers publish current values. Reference ET values forTulelake, McArthur, and Alturas are calculated dailyby the California Department of Water Resources(DWR) and can be obtained through DWR’sCalifornia Irrigation Management InformationSystem (CIMIS). You can use these ET values for otherlocations in the Intermountain Region by selecting thelocation with weather conditions most similar to those

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

3/2 3/16 3/30 4/13 4/27 5/11 5/25 6/8 6/22 7/6 7/20 8/3 8/17 8/31 9/14 9/28 10/12

Alfa

lfa W

ater

Use

- E

T (

inch

es/d

ay)

1993 Historic Average


Figure 4.5. Comparison of daily water use by alfalfa: 1993 season and long-term average.

in your area. The reference values are based on pastureuse, however. You must modify them to estimate alfal-fa water use before using the values for irrigationscheduling. UC Farm Advisors can assist you with theconversion. In most situations, historical long-termaverages of water use by alfalfa suffice for irrigation-scheduling purposes. Table 4.2 shows average long-term water use values for Tulelake. Adjust long-termaverages to reflect current weather conditions, sinceweather can vary significantly from year to year andthere is no such thing as an “average” year. For exam-ple, contrast the daily water use shown in Figure 4.5with the long-term average daily use.

When to IrrigateAt the start of the production season, the soil profile isfilled with water from rainfall or irrigation. From thatpoint on, the grower tracks daily crop water use andkeeps a running total of it. Once total crop water use,or total soil water depletion, equals or approaches theallowable depletion, the field should be irrigated(Figure 4.6). After irrigating and refilling the soil-waterreservoir, daily crop water use is again calculated andadded to the total water use to date. Another irrigationis scheduled when soil-water depletion since the lastirrigation approaches the allowable depletion. Figure4.7 summarizes the steps of the water budget method.

Water requirements of alfalfa are based on weather

conditions and do not change because of soil type.Many believe that alfalfa grown on sandy soil needsmore water than that grown on another type of soil.The fact is that alfalfa grown on sandy soil does notneed more total water; it does, however, need irriga-tion more frequently and at lower volume (for a short-er set time or with smaller nozzles). This is so becausesandy soil has less water storage capacity than do othersoil types. Table 4.3 shows minimum recommendedirrigation frequencies for different soil types in theIntermountain Region. The recommendations arebased on historical data on crop-water use. Looking atTable 4.3, compare the irrigation frequency for a sandysoil to that for a clay soil. During July for example, a


Figure 4.6. The water budget method. Daily ET is accumulateduntil the allowable depletion is reached. The field is then irrigatedto refill the soil-water reservoir.

Table 4.2. Average weekly and daily water use by alfalfa in theTulelake Basin.1

W E E K B E G I N N I N G W E E K LY D A I LY

( M O . A N D D AY ) TOTA L ( I N . ) AV E R A G E ( I N . )

3/15 0.10 0.01

3/22 0.32 0.05

3/29 0.59 0.08

4/5 0.83 0.12

4/12 0.95 0.14

4/19 1.04 0.15

4/26 1.13 0.16

5/3 1.22 0.17

5/10 1.30 0.19

5/17 1.39 0.20

5/24 1.48 0.21

5/31 1.57 0.22

6/7 1.66 0.24

6/14 1.76 0.25

6/21 1.91 0.27

6/28 2.05 0.29

7/5 2.13 0.30

7/12 2.18 0.31

7/19 2.14 0.30

7/26 2.05 0.29

8/2 1.93 0.28

8/9 1.81 0.26

8/16 1.69 0.24

8/23 1.56 0.22

8/30 1.44 0.21

9/6 1.33 0.19

9/13 1.19 0.17

9/20 1.07 0.15

9/27 0.95 0.14

10/4 0.85 0.12

1. Based on long-term average weather data

Allowable depletion

Available soil- water

Day 1Day 2Day 3Day 4Day 5Day 6Day 7

Period ET (in.)

.28

.27

.30

.32

.30

.28

.25

7 2.0Total

When to irrigate? How much to apply ?

After 7 days 2.0 in. (net)

fine sand or loamy sand must be irrigated every 7 days,while a clay soil must be irrigated every 15 days.

Compensating for production practices and limitationsThe water budget theory of irrigation scheduling is rel-atively straightforward, but alfalfa production practicescomplicate putting the theory into practice. For exam-ple, cutting affects water use by alfalfa. Generally, wateruse is near zero immediately after cutting and risesslowly after a few days, as the crop begins to grow. Afterabout 10 days, alfalfa regrowth fully covers the groundand full crop water use resumes. A grower must com-pensate for this reduction in water use after cutting orhe or she will overirrigate. Sophisticated methods forcalculating the reduction are available, but a practicalmethod is to consider alfalfa water use to be zero for 5 days after cutting. After 5 days switch to full-use estimates until alfalfa is cut again. (See Studying aPractical Example, later in this chapter, to understandhow this rule of thumb is applied.)

Harvesting and curing operations also complicateirrigation scheduling. Water cannot be applied tooclose to a cutting because irrigation wets the soil. Onwet ground, harvest equipment may get stuck and ismore likely to cause wheel ruts and compaction. Also,alfalfa that is cut and laid on moist soil to dry will cure


Water Budget Irrigation Scheduling

1. Estimate daily crop water use by using publisheddaily estimates, data from CIMIS, or tables oflong-term average crop water use (see Table 4.2for an example).

2. Add the daily water use to the running total ofwater use to date. The result is the soil waterdepletion to date.

3. Subtract any water additions—irrigations orrainfall—from soil-water depletion to date.

4. Schedule irrigation to replace the accumulatedwater use by the crop.

The goal: Keep soil-water depletion above theallowable depletion, without adding water in excessof the water-holding capacity of the soil.Remember that letting the soil dry beyond theallowable depletion results in lost yield and thatapplying more water than the soil can hold leachesnutrients and wastes energy and water.

Figure 4.7. The steps of irrigation scheduling according to the waterbudget method.

Table 4.3. Recommended irrigation frequencies for alfalfa produced on different soil types in the Intermountain Region. (see notes below.)

I R R I G AT I O N F R E QU E N C Y 1

( D AY S B E T W E E N I R R I G AT I O N S )

I R R I G AT I O NS O I L T Y P E A M O U N T 2 A P R . M AY J U N E J U LY AU G . S E P T.

Coarse sand 1.00 7 5 4 3 4 6

Fine sand, loamy sand 2.00 14 10 8 7 8 12

Sandy loam 3.00 21 15 13 10 12 18

Fine sandy loam, loam, silt loam 4.00 29 20 17 13 15 24

Clay-loam, silty clay 4.40 – 22 18 15 17 26

Clay 4.60 – 23 19 15 18 27

Organic clay loams 8.00 – – 33 27 31 –

Daily crop water use (in.) .14 .20 .24 .30 .26 .17

1. Irrigation frequency is calculated by dividing the irrigation amount, or allowable depletion, by daily crop water use.2. Irrigation amount is the net amount of water to apply (the allowable depletion for that soil type from Table 4.1 multiplied by 4 ft of rooting depth). The actual

amount that should be applied is the net amount in the table divided by the irrigation efficiency. (This accounts for inefficiencies in the irrigation system and isexplained in detail later.)

Notes:a. The values in the table are based on irrigations occurring when 50% of the available soil moisture is depleted (50% allowable depletion).b. For the months where no values are listed, irrigation scheduling should be based on soil moisture monitoring. Dashes mean that the soil-water-holding capacity

is so great that irrigation frequency is significantly less than once per month.c. For the early part of the year, use soil moisture monitoring to determine the first irrigation. The values in this table can then be used to determine the time of

subsequent irrigations.

very slowly. The preferred interval between irrigationand cutting depends on soil type. It may be as short as2 days for sandy soils and as long as 10 to 15 days forfine-textured clay soils. Furthermore, fields obviouslycannot be irrigated while alfalfa is curing, which typi-cally requires from 5 to 8 days.

Because cutting delays irrigation, fields usually needwater as soon after cutting as possible. Alfalfa is mostsensitive to water stress when regrowth begins aftercutting. When irrigation is postponed after cutting,dramatic yield reductions can result.

So, to summarize: (1) Fields should not be irrigatedtoo close to cutting, and (2) fields should be irrigatedas soon as possible after the hay has cured and beenremoved from the field. (The practical example later inthis chapter shows how irrigation scheduling can beadjusted to allow for harvesting and curing.)

To account for seasonal differences in water require-ments, growers must either change irrigation frequen-cy or change set times to adjust the amount of waterapplied per irrigation (or both). Two 12-hour sets perday prevail in wheel-line- and hand-line-irrigated alfalfa fields in the Intermountain Region. (Thougheach set is described as 12 hours long, actual irrigationtime is shortened by the amount of time workers take,between sets, to move the lines.) Longer or shorter settimes are unusual because of labor constraints and thedifficulty of moving irrigation lines at night. Set timesfor flood-irrigated fields are also inflexible; they aredetermined by the length of time required for thewater to travel from the head to tail end of the field.Therefore, the most convenient method for schedulingalfalfa irrigations is to vary the irrigation frequency orthe number of days between irrigations (see Table 4.3).

However, sometimes the number of days betweenirrigations is fixed because of delivery or irrigation sys-tem limitations. Under these conditions, record theaccumulated crop water use between irrigation dates.Adjust irrigation set times to deliver the amount ofwater that has been depleted since the last irrigation.

Whenever using the water budget method to scheduleirrigations, monitor soil moisture regularly to “ground-truth” the accuracy of the water budget method.

Studying a practical exampleAn example should help clarify the preceding discus-sion on practical irrigation scheduling. To follow alongwith this example, refer to the accompanying water use

table, Table 4.4, and to the graph of soil-water deple-tion, Figure 4.8. This example relates to a healthy,well-established alfalfa field on sandy loam soil in theTulelake region.

On May 12, the field was given a 12-hour irriga-tion that supplied 2.4 inches of water (net). This irrigation completely refilled the soil profile, so thesoil-water depletion on this date was 0.00 (see point Aon the table and graph). For 6 days, the crop wasassumed to use water in amounts typical for theregion (Table 4.2 supplies this information). The aver-age crop water use was added each day to the soildepletion balance. On May 18 the field received 0.50inch of rain, so 0.50 inch of water was subtractedfrom 0.96, the soil depletion balance. The daily cropwater use, 0.20 inch, was then added. So, soil-water

depletion on May 18 (point B) was calculated to be0.66 inch (0.96 – 0.50 + 0.20 = 0.66).

After May 18, average crop water use figures wereagain added each day to the soil-water depletion bal-ance. On May 26 (point C) the accumulated depletiontotaled 2.29 inches. Because this soil depletion approxi-mated the net amount applied in a 12-hour irrigation,the field was irrigated the next day, May 27. On thatday, the 2.4-inch application of water was subtractedfrom 2.29, the soil depletion balance; 0.21 inch of aver-age crop water use was added, resulting in a net soil-water depletion of 0.10 inch (point D). Important note:The 2.29 inches of soil-water depletion that occurredbefore the May 27 irrigation was less than the 3 inchesof allowable depletion for this sample sandy loam soil(Table 4.1). Therefore, no yield reduction occurred dueto moisture stress prior to this irrigation. The irrigation


The objective of the waterbudget is to maintain soil

moisture near the optimumlevel by keeping track of cropwater use and then irrigating

to replace the water used.


Table 4.4. Water use table for a sample alfalfa field, Tulelake area.

C RO P R A I N S O I L C RO P R A I N S O I L WAT E R O R WAT E R WAT E R O R WAT E R

U S E I R R I G AT I O N D E P L E T I O N U S E I R R I G AT I O N D E P L E T I O ND AT E ( I N . ) ( I N . ) ( I N . ) E V E N T D AT E ( I N . ) ( I N . ) ( I N . ) E V E N T

A 5/12 0.19 2.4 0.00 12-hour irrigation 6/22 0.27 0.33

5/13 0.19 0.19 6/23 0.27 0.60

5/14 0.19 0.38 6/24 0.27 0.87

5/15 0.19 0.57 6/25 0.27 1.14

5/16 0.19 0.76 6/26 0.27 1.41

5/17 0.20 0.96 6/27 0.27 1.68

B 5/18 0.20 0.5 0.66 0.5 in. rain 6/28 0.29 1.97

5/19 0.20 0.86 6/29 0.29 2.26

5/20 0.20 1.06 I 6/30 0.29 2.4 0.15 12-hour irrigation

5/21 0.20 1.26 7/1 0.29 0.44

5/22 0.20 1.46 7/2 0.29 0.73

5/23 0.20 1.66 7/3 0.29 1.02

5/24 0.21 1.87 7/4 0.29 1.31

5/25 0.21 2.08 7/5 0.30 1.61

C 5/26 0.21 2.29 7/6 0.30 1.91

D 5/27 0.21 2.4 0.10 12-hour irrigation 7/7 0.30 2.21

5/28 0.21 0.31 J 7/8 0.30 2.4 0.11 12-hour irrigation

5/29 0.21 0.52 7/9 0.30 0.41

5/30 0.21 0.73 7/10 0.30 0.71

5/31 0.22 0.95 7/11 0.30 1.01

6/1 0.22 1.17 7/12 0.31 1.32

6/2 0.22 1.39 K 7/13 0.31 1.2 0.43 6-hour irrigation

6/3 0.22 1.61 First cutting 7/14 0.31 0.74

E 6/4 0.00 1.61 7/15 0.31 1.05

6/5 0.00 1.61 7/16 0.31 1.36

6/6 0.00 1.61 7/17 0.31 1.67 Second cutting

6/7 0.00 1.61 L 7/18 0.00 1.67

6/8 0.00 1.61 7/19 0.00 1.67

6/9 0.24 1.85 7/20 0.00 1.67

6/10 0.24 2.09 7/21 0.00 1.67

F 6/11 0.24 2.33 7/22 0.00 1.67

G 6/12 0.24 2.4 0.17 12-hour irrigation 7/23 0.30 1.97

6/13 0.24 0.41 7/24 0.30 2.27

6/14 0.25 0.66 M 7/25 0.30 2.4 0.17 12-hour irrigation

6/15 0.25 0.91 7/26 0.29 0.46

6/16 0.25 1.16 7/27 0.29 0.75

6/17 0.25 1.41 7/28 0.29 1.04

6/18 0.25 1.66 7/29 0.29 1.33

6/19 0.25 1.91 7/30 0.29 1.62

6/20 0.25 2.16 7/31 0.29 1.91

H 6/21 0.27 2.4 0.03 12-hour irrigation 8/1 0.29 2.20

occurred 7 days before the first cutting, on June 3,allowing ample time for the soil to dry for harvest.

As explained earlier, it is acceptable to assume thatfor 5 days after cutting, crop water use is zero. Afterthat time switch to using full-use estimates. In thisexample crop water use was estimated as zero fromJune 4 through June 8 (period E). On the sixth dayfollowing cutting, June 9, the use of full-use estimatesresumed.

After soil-water depletions totaled 2.33 inches onJune 11 (point F), irrigation was applied on June 12(point G). This allowed ample time for the hay to cureafter cutting on June 3. In a similar manner, normalirrigations were scheduled for June 21 and 30 and July8 (points H, I, andJ). Irrigations were more frequentduring this period because of the increased waterdemand of midsummer.

On July 13 (point K), an early irrigation consistingof 1.2 inches, half the normal amount of water, wasapplied. If this irrigation had been delayed until 2.4inches of water had been depleted, the irrigation

would have been too close to the second cutting, onJuly 17. The early, partial irrigation was scheduled tocarry the alfalfa through the postharvest period with-out a water deficit. Again allowing for zero crop wateruse for 5 days after cutting (period L), the next irriga-tion was scheduled for July 25 (point M).

A D J U S T M E N T S TO A C H I E V EU N I F O R M I T Y A N D E F F I C I E N C Y

Information on crop water use (Table 4.2) indicatesthe net water requirement of alfalfa, not the actualamount that should be applied. The amount of waterin an irrigation must supply crop water requirementsas well as compensate for inefficiencies in the irrigationsystem. Irrigation water can be lost from runoff; deeppercolation (movement of water below the root zoneof the crop); and, in the case of sprinklers, spray evapo-ration and drift. Most irrigation water losses are attrib-utable to nonuniformity of water application. If every


Figure 4.8. Soil-water depletion in sample alfalfa field, Tulelake area.

2.50

2.00

1.50

1.00

0.50

0.00

Soil

Moi

stur

e De

plet

ion

(in.)

5/12

5/16

5/20

5/24

5/28 6/1

6/5

6/9

6/13

6/17

6/21

6/25 7/3

6/29 7/7

7/11

7/15

7/19

7/23

7/27

7/31

A

B

C

D

F

G HI J

L

Firs

t Cut

ting

E

Seco

nd C

uttin

g

K

M

part of the field received the same amount of water,uniformity would be 100 percent. However, no irriga-tion is perfectly uniform—some parts of the fieldreceive more water than do others. To compensate fornonuniformity, some parts of the field must be overir-rigated so that others will be adequately irrigated. Toavoid underirrigation of large areas of the field, use theequation that follows to calculate the gross irrigationrequirement—that is, the amount of water needed tomeet plant needs (crop water needs) and compensatefor irrigation inefficiency.

Grossirrigation =

Net irrigation requirement

requirement Irrigation system efficiency

Irrigation system efficiencyFor example, if the alfalfa uses 4 inches of water (that is,if the net irrigation requirement is 4 inches) and the sys-tem efficiency is 80 percent, the application required tomeet plant needs is 5 inches (4 inches ÷ 0.8 = 5 inches).

The efficiency of an irrigation system is difficult tomeasure. Numerous field studies show however, thatan irrigation efficiency of 75 percent can be used tocalculate gross irrigation requirement when irrigatingwith wheel-line or hand-move sprinkler systems. Use85 percent when irrigating with center-pivot machines(Table 4.5). The irrigation efficiency of flood systemsvaries from 65 to 80 percent, depending on soil type,slope, border length, and other factors. Select a valuewithin this range based on knowledge of your irriga-tion system.

A P P L I C AT I O N R AT E

Knowing how much water the crop needs is of littlebenefit if you do not know how much water is beingapplied in an irrigation. Knowledge of the applicationrate is a prerequisite to using the water budget method.

The application rate can be calculated from the irri-gation system flow rate. Several methods are availableto ascertain the flow rate of an irrigation system. On awhole-field basis, a flow meter is the most precise andconvenient means where the water supply is deliveredin pipes. The drawback to flow meters is their cost(approximately $800 or higher, depending on pipediameter). Flow rates can also be estimated by usingthe pump capacity or with data collected from a pump

test (often performed by utility companies). Flumesand weirs are used to determine the flow rate for sys-tems where ditches deliver water. (Flow rates and watervolumes are often expressed in different units, but eachcan be easily converted—see Table 4.6.)

After you know the flow rate, you are ready to calculate application rate. The calculation you usedepends on the type of irrigation system you have.

Wheel-Line and Hand-Move Sprinkler Systems

To calculate the application rate for one of these sys-tems, use the following equation:

Application rate (in./hr.) =96.3 x QSm x Sl

whereQ = average sprinkler discharge, expressed in

gallons per minute (gpm)Sm = spacing along the main line (that is, the dis-

tance between moves) expressed in feetSl = spacing along lateral (that is, the distance

between sprinklers) expressed in feetFigure 4.9 presents an example that uses the

equation.To determine sprinkler discharge, divide the system

flow rate by the number of sprinklers or slip a hose overa nozzle and measure the volume of water collected in a


Table 4.5. Typical application efficiencies for different irrigationsystems.

A P P L I C AT I O NS Y S T E M E F F I C I E N C Y

Sprinkler

Wheel line 65–80

Hand line 70–80

Center pivot 75–90

Flood

Border strip 65–80

Table 4.6. Conversions useful when scheduling irrigation.

1 acre-inch = 27,154 gallons

1 acre-foot = 325,848 gallons

1 cubic ft per second (CFS) = 449 gpm

1 CFS = approx. 2 acre-feet per day

1 CFS = approx. 1 acre-inch per hour

given time period. Or, as an alternative to using theequation above, you can estimate application rate for asprinkler system from irrigation tables provided youknow the nozzle size, pressure and sprinkler spacing.(Table 4.7).

The average depth of water applied during an irriga-tion is estimated by multiplying the application rate,in inches per hour, by the set time in hours.

Center-Pivot Systems

The equation that follows will allow you to calculatethe average depth of water applied per revolution of acenter-pivot irrigation system:

Depth applied (in.) = Q x H449 x A

whereQ = flow rate, expressed in gpmH = hours per complete revolutionA = area irrigated with pivot, expressed in acresFigure 4.10 is an example that employs the equation.

Border-Strip Flood Systems

The average depth of water applied per set with aflood-irrigation system is calculated as follows.

Depth applied (in.) = Q x T449 x A

whereQ = flow rate, expressed in gpmT = irrigation set time, in hoursA = area, in acresFigure 4.11 shows how to apply the equation.


Table 4.7. Sprinkler application rate (in./hr.) for 40- by 60-ft spacing.

N O Z Z L E A P P L I C AT I O N R AT E ( I N / H R )S I Z E ( I N ) 4 0 P S I 5 0 P S I 6 0 P S I

3/32 .06 .07 .08

7/64 .09 .10 .11

1/8 .11 .13 .14

9/64 .15 .16 .18

5/32 .18 .20 .22

11/64 .22 .25 .27

3/16 .26 .29 .32

13/64 .31 .34 .38

7/32 .36 .40 .44

Figure 4.9. Sample calculation to determine the application rate of awheel-line or hand-move sprinkler system.

Figure 4.10. Sample calculation to determine average depth of waterapplied by a center-pivot system.

Flow rate = 900 gpmHr/revolution = 70 hrArea irrigated = 125 acres

Average depth applied per revolution:

D =900 gpm x 70 hr449 x 125 acres

= 1.12 in./revolution

Note: Acreage under pivot is equal to (r)2 x 3.14

43,560where: r = radius of the pivot (ft)

Figure 4.11. Sample calculation to determine the average depth ofwater applied by a flood-irrigation system.

Flow rate = 1,120 gpmSet time = 8 hr

Area irrigated = 3.6 acres

Average depth applied:

D =1,120 gpm x 8 hr 449 x 3.6 acres

= 5.54 in.

Pump capacity = 675 gpmNumber of sprinklers = 96

Main line spacing = 60 ftLateral spacing = 40 ft

Set time = 12 hr

Average application rate:

Q =675 gpm 96 sprinklers

= 7 gpm/sprinkler

in./hr = 96.3 x 7 gpm 40 ft x 60 ft

= 0.28 in./hr.

Average depth applied:D = 0.28 in./hr x 12 hr

= 3.36 in. total

S Y S T E M D E S I G N R E Q U I R E M E N T S

The key to efficient irrigation management begins withthe irrigation system and its flow rate. The system flowrate of many irrigation systems in the IntermountainRegion is inadequate. To fully meet crop needs, the sys-tem flow rate must be sufficient to irrigate the field ade-quately during the period of peak evapotranspiration(typically July) without exceeding the allowable soilmoisture depletion. The following equation can beused to calculate the necessary flow rate:

Q = 449 x A x DT

whereQ = flow rate, expressed in gpmA = area irrigated in acresD = gross depth of water to be applied, in inchesT = actual irrigation time, in hours

The interval between irrigations is determined bydividing the allowable soil moisture depletion by thedaily peak ET rate (from Table 4.2). The gross depth of water to be applied is the allowable soil moisturedepletion divided by the irrigation efficiency of thesystem (discussed in previous section). The hours ofirrigation is the time required to irrigate the field. Thefewer the hours of irrigation, the higher the flow rateneeds to be.

Figure 4.12 presents a system flow rate calculationtypical of the Intermountain Region. A grower needs326 gallons per minute to irrigate a 40-acre alfalfafield. This equates to 8 gallons per minute per acre ofwheel-line-irrigated alfalfa. The required flow ratewould be slightly less (approximately 7.5 gpm) for irri-gation systems that do not involve downtime duringwhich the lines are moved.

I R R I G AT I O N S Y S T E MI M P RO V E M E N T S

Sprinkler Systems

System design factors that affect irrigation efficiencyinclude sprinkler spacing, operating pressure, pressuredifferences throughout the system, and nozzle type and

size. Several changes in system design improve unifor-mity and performance of sprinklers (Figure 4.13).

The most common sprinkler spacing in inter-mountain alfalfa fields is 40 by 60 feet (in otherwords, 40 feet between sprinkler heads and 60 footmoves). Numerous field evaluations show that thisspacing results in good uniformity when large ( 11⁄64 orlarger) sprinkler nozzles are used under low to moder-ate wind conditions.

Sprinkler pressure should be above 35 pounds persquare inch (psi). Minimize pressure losses due to fric-tion in the lateral lines by using appropriate pipe diam-eters. The most common lateral pipe diameter is 4

inches. However, pressure losses can be greatly reduced—and energy saved—by using 5-inch diameter pipe forlaterals. Analyze pressure losses due to friction in themain line as well; change the pipe size if necessary.

Select the proper nozzle type. Types of nozzlesinclude standard circular orifices, low-pressure nozzles,and flow-control nozzles. Field evaluations reveal thatstandard nozzles are adequate for systems with pres-sures of 35 psi or greater. Use flow-control nozzles forsystems with pressure losses exceeding 20 percent ofthe design pressure.

Wind lowers the uniformity of sprinkler systems bydistorting the spray pattern of sprinkler nozzles. Itsimpact can be significant, especially when wind veloci-ty is high. Changes, such as closer spacing or lowerpressure, can lessen the effects of wind, but its impactcannot be completely eliminated. Sprinkler systemsthat move continuously (that is, center-pivot or linear-move systems) are not as affected by wind as are wheel-line or hand-move systems.


Knowing how much water the crop needs is of little

benefit if you do not knowhow much water is applied

in an irrigation.

Flood Systems

The uniformity of flood irrigation depends on howlong water stands or ponds on the soil surface at vari-ous distances along the border length. The longer theponding time at a particular distance, the more waterinfiltrates. The ponding time depends on how fast thewater flows to the end of the field (this speed is deter-mined by border length, inflow rate, infiltration rate,slope, and surface roughness) and how fast the waterdisappears after the irrigation water is cut off.

Generally, water stands longer along the upper part ofa field than along the lower part, resulting in moreinfiltration along the upper part.

Uniformity of flood systems can be improved bygetting the water to the end of the field faster. Toimprove uniformity, use higher flow rates into the bor-der, shorten border lengths, and improve land leveling.The higher the flow rate, the faster water flows to theend of the field and the more uniform the application.The appropriate field length depends on soil type(Table 4.8). Field lengths for clay loam soils should notexceed 1⁄4 mile; field lengths for sandy soils should notexceed 1⁄8 mile. The width should be compatible withthe system flow rate and also with the harvestingequipment. Many of these efforts to increase uniform-ity may increase surface runoff, thus requiring a tail-water return system to capture and reuse the runoff.Failure to do so could result in higher pumping costsand increased water use.


• Determine the application rate and averagedepth of water applied.

• Irrigate during low-wind periods when feasible.(The uniformity of irrigation is greatly reducedat wind speeds greater than 10 to 15 mph.)

• Offset lateral locations to improve seasonal uniformity.

• Use flow-control nozzles when the pressure vari-ation between the first and last nozzle exceeds 20 percent.

• Repair leaks and malfunctioning nozzles.• Maintain adequate pressure (above 35 psi at the

last nozzle for wheel lines) by adjusting thepump impeller of semi-open impellers, repairingor replacing a worn pump, or reducing the num-ber of laterals operating.

• Use the same nozzle size throughout the irrigation system.

• Use closer spacing, boom-mounted nozzles,and/or rotating-type nozzles for center-pivotsystems.

Figure 4.12. Sample calculation to determine the system flow ratefor a 40-acre alfalfa field.

Figure 4.13 Ways to improve uniformity and efficiency of sprinklerirrigation systems.

Type of irrigation system = wheel-line sprinkler

Allowable soil moisture depletion = 3.0 in.Peak ET = 0.3 in./day

Irrigation efficiency = 75 percent

1. Interval between irrigations

= Allowable soil moisture depletionPeak ET

3.0 in. = 10 days0.3 in./day

2. Hours of operation for an irrigation system operated continuously except during moving

= 22 hr/day x 10 days= 220 hr

3. Gross depth

= 3 in.irrigation efficiency

= 3 in.0.75

= 4 in.

4. System flow rate

= 449 x 40 acres x 4.0 in.220 hr

= 326 gpm

5. Required flow rate

= 326 gpm40 acres

= 8 gpm per acre (approx.)

I R R I G AT I O N S T R AT E G I E S F O RL I M I T E D WAT E R S U P P L I E S

Sometimes the supply of irrigation water (from apumping plant or an irrigation district) is insufficientto supply the full seasonal water requirements of alfal-fa. When this occurs, irrigate fully in the spring ratherthan trying to “spread out” an insufficient water sup-ply and deficit-irrigate for the entire season. Theamount of irrigation water required per ton of alfalfa isless for the first cutting than for the second or third.Temperatures are cooler in the spring and the chanceof rainfall is greater. First-cutting yields usually surpasssecond- and third-cutting yields. Also, the quality and

price of first-cutting hay is usually higher than those ofsecond-cutting hay.

Research and field experience throughout much ofCalifornia have demonstrated that irrigation water canbe withdrawn or reduced following the first cuttingwithout significantly reducing stand density or yieldsthe following year. Deficit irrigating forces alfalfa intoa drought-induced dormancy. The stand usually recov-ers fully when it receives adequate water the next pro-duction season.


Browers, W. O., R. L. Snyder, S. B. Southard, and B. J. Lanini.1989. Water-holding characteristics of California soils. Oakland:University of California Division of Agriculture and NaturalResources, Leaflet 21463.

Goldhammer, D. A., and R. Snyder, eds. 1989. Irrigation schedul-ing. Oakland: University of California Division of Agricultureand Natural Resources, Leaflet 21454.

Hanson, B. R., D. B. Marcum, and R. W. Benton. 1986.Irrigating alfalfa for maxiumum profit. Proceedings, 16thCalifornia Alfalfa Symposium, 36–43. December 11–12,Sacramento, CA.

Stewart, B. A., and D. R. Nielsen, eds. 1990. Irrigation of agricul-tural crops. Madison, WI: American Society of Agronomy,Crop Science Society of America, and Soil Science Society ofAmerica, Inc. Number 30.


Table 4.8. Suggested field lengths and unit flow rates for border orflood irrigation of slopes of 0.1 to 0.2 percent.

U N I T L E N G T H F L OW R AT E

S O I L T Y P E ( F T. ) ( G P M / F T. O F W I D T H )

Clay 1,300 7–10

Clay loam 1,300 10–15

Loam 1,300 25–35

Loam 600 15–20

Sandy loam 600 25–30

Sandy 600 30–40

Source: 1974. Border Irrigation. SCS National Engineering Handbook,Section 15. Washington, DC.

41

C H A P T E R F I V E

F E RT I L I Z AT I O NRoland D. Meyer, Daniel B. Marcum, and Steve B. Orloff

�roviding an adequate supply of nutrients isimportant for alfalfa production and isessential to maintain high and profitable

yields. However, proper plant nutrition can be a com-plex and often difficult management process. Theprocess includes an analysis of which nutrients areneeded, selection of the proper fertilizer, applicationtiming and placement, economics, record keeping,and environmental considerations. This chapter servesas a guide to alfalfa fertilization in the IntermountainRegion and includes information on appropriatemethods of sampling alfalfa and interpreting soil andtissue tests.

Before applying fertilizer to alfalfa, examine otherfactors affecting yield. It makes little sense to fertilizewith a nutrient when another factor is more limitingto plant growth. For example, an application of sulfur,even when sulfur is deficient, may not increase yieldsif water is not sufficient to allow plants to grow inresponse to applied fertilizer.

Since historical trends help with management deci-sions, thorough, well-organized records of plant tissueand soil-test information are important. Recordsshould include information about date of sampling;crop yield and fertilizer history; and, most important-ly, the location of the samples.

E S S E N T I A L P L A N T N U T R I E N T S

Seventeen elements are needed, in varying amounts,for plant growth. Carbon, hydrogen, and oxygencome from water and from carbon dioxide in the air.The other 14 elements are obtained from either thesoil or fixation of atmospheric nitrogen by bacteria inroot nodules. Another nutrient, cobalt, is essential tolegumes, for nitrogen fixation. Growth slows or stopswhen a plant is unable to obtain one or more of theseelements. Thus, all nutrients must be available to theplant in adequate quantities throughout the produc-tion season. The nutrients that are most commonlyneeded are sulfur, followed closely by phosphorus,then potassium, boron, and molybdenum (Table 5.1).

DA

N M

AR

CU

M

D I A G N O S I S O F N U T R I E N T D E F I C I E N C I E S

A key aspect of designing a fertilization program isevaluating the nutrition status of the alfalfa. This canbe done by visual observation, soil analysis, or planttissue testing. Using all three in combination providesthe best results.

Visual Observation

Nutrient deficiencies may exhibit visual plant symp-toms such as obvious plant stunting or yellowing.Table 5.2 summarizes visual symptoms of commondeficiencies. (Also see color photos 5.1 through 5.7.)Unfortunately, visual symptoms are not definitive andcan be easily confused or mistaken for symptomscaused by other factors—insect injury, diseases,restricted root growth. The other problem with usingvisual observation of plant symptoms to diagnosenutrient deficiencies is that significant yield losses mayhave already occurred by the time the symptomsappear. Always confirm visual diagnosis with laborato-ry diagnosis or test strips with selected fertilizers.

Laboratory Analysis

Both soil and plant tissue test results are used to detectplant nutrient deficiencies. These two tests differ intheir ability to reliably diagnose nutrition problems inalfalfa (Table 5.3). To fully understand and correctproblems, test both soil and tissue.

Soil testing

Soil tests provide an estimate of nutrient availabilityfor uptake by plants and are most useful for assessingthe fertility of fields prior to planting. Soil samplingmethods are critical, since soil samples must adequate-ly reflect the nutrient status of the field. Because a rep-resentative sample of an entire field gives an average ofall the variation in that field, it is not the best way todevelop recommendations for parts of the field thatare less productive. The best technique is to divideeach field into two or three areas representing good,medium, and poor alfalfa growth. Within each areaestablish permanent benchmark locations approxi-mately 50 x 50 feet in size (Figure 5.1). To ensure that


Table 5.1. Nutrition needs of alfalfa in the Intermountain Region.

E L E M E N T F E RT I L I Z E RN E E D E D S Y M B O L R E QU I R E D 1

Nitrogen N Seldom

Phosphorus P2O5 Frequently

Potassium K2O Less frequently

Calcium Ca Never

Magnesium Mg Never

Sulfur S Frequently

Iron Fe Seldom

Manganese Mn Never

Chlorine Cl Never

Boron B Less frequently

Zinc Zn Never

Copper Cu Never

Molybdenum Mo Less frequently

Nickel Ni Never

Cobalt Co Never2

1. Frequently: Over 25% of the acreage shows need for fertilization with thisnutrient.Less frequently: Less than 25% of the acreage shows need for fertilization.Seldom: Less than 1% of the acreage shows need.Never: A deficiency has never been reported or observed.

2. Necessary for nitrogen fixation only.

Table 5.3. Relative reliability of soil and plant tissue testing fornutrient deficiency.

NUTRIENT SOIL TESTING TISSUE TESTING

Sulfur Very poor Excellent

Phosphorus Good Excellent

Potassium Good Excellent

Boron Poor Excellent

Molybdenum Not recommended Excellent

Table 5.2. Nutrient deficiency symptoms observed in alfalfa.

DEFICIENCY SYMPTOMS

Nitrogen Generally yellow, stunted plants

Phosphorus Stunted plants with small leaves; some-times leaves are dark blue-green

Potassium Pinhead-sized yellow or white spots onmargins of upper leaves; on more matureleaves, yellow turning to brown leaf tipsand edges

Sulfur Generally yellow, stunted plants

Boron Leaves on the upper part of plant are yel-low on top and reddish purple on theunderside; internodes are short

Molybdenum Generally yellow, stunted plants

f e r t i l i z a t i o n 43

you will be able to find each benchmark area again,describe it in relation to measured distances to specificlandmarks on the edge of the field. By using thismethod to collect soil and plant tissue samples, youwill be able to compare areas of the field with differentproduction levels, develop appropriate managementresponses, and track changes over the years.

The best time to sample soil is soon after an irriga-tion or rainfall, so the probe easily penetrates the moistsoil. Before taking a soil sample, remove debris orresidual plant material from the soil surface. The sam-ple can be taken with a shovel, but an Oakfield tube orsimilar sampling probe is preferred. Sample the top 6to 8 inches of soil. Take 15 to 20 cores at random fromeach benchmark area and mix them thoroughly in a

plastic bucket to produce a single 1 pint compositesample for each benchmark area. Place each sample ina separate double-thick paper bag and dry the soil atroom temperature before mailing to the laboratory. Toget a complete profile of the nutrition status of an alfal-fa field, perform all the soil and tissue tests cited inTable 5.4. A list of laboratories is found in Universityof California Special Publication 3024, CaliforniaCommercial Laboratories Providing Agricultural Testing.

Taking soil samples every year may not be necessaryonce historical trends have been established. Samplingbenchmark areas every time alfalfa is planted is usuallysufficient to establish trends. If poor alfalfa growth isobserved in other parts of the field, take samples fromboth good and poor growth areas so the fertility level ofthe two areas can be compared. Table 5.5 lists guide-lines for interpreting soil tests. Values are given fordeficient, marginal, adequate, and high levels. An eco-nomic yield response to fertilizer application is verylikely for values below the deficient level, somewhatlikely for values in the marginal level, and unlikely forvalues over the adequate level.

Plant tissue testing

By far the most precise method of determining thenutrient needs of alfalfa is plant tissue testing. Suchtests are the best reflection of what the plant has takenup and are far more accurate than soil tests, particular-ly for sulfur, boron, and molybdenum. Plant tissuetests are useful in monitoring the nutrition status andevaluating the effectiveness of current fertilizationpractices.

The best time to take a tissue sample is when thecrop is in the 1⁄10 bloom growth stage or when regrowthmeasures 1⁄4 to 1⁄2 inch in length. (Alfalfa is often cutprior to 1⁄10 bloom to attain high-quality forage.)

Figure 5.1. Sound soil and plant tissue-testing procedure involvesestablishing permanent benchmark sampling locations (50 x 50 feetin size) within areas of the field that support good, medium, andpoor alfalfa growth. Define these benchmark areas in relation tomeasured distances to specific landmarks on the edge of the field.

Medium

Poor

Good

50 x 50 foot permanent benchmark areas

Permanentmarkers (trees,telephone orelectric poles,fence posts)

290 ft.

250 ft.

Table 5.4. Suggested tests for a complete examination of soil andalfalfa tissue.

SOIL PLANT TISSUE

pH1 Sulfur (SO4–S)

Phosphorus Phosphorus (PO4–P)

Potassium Potassium

ECe1 Boron

Calcium, magnesium, sodium1 Molybdenum

SAR1 Copper

1. These tests evaluate factors that affect the availability of nutrients and thepresence of undesirable salt levels. ECe ( electrical conductivity of satura-tion extract (mmho/cm). SAR ( Sodium absorption ratio)

Plant tissue testing . . . by far the most precise

method of determining thenutrient needs of alfalfa.

When alfalfa is cut prior to 1⁄10 bloom (for example,bud stage) nutrient concentrations should be approxi-mately 10 percent higher than when sampled at 1⁄10

bloom. Samples can be collected at any cutting, butcollection at first cutting is preferred because it is thebest time to detect a sulfur deficiency. Collect 40 to 60stems from at least 30 plants in each of the benchmarkareas.

Different plant parts are analyzed for different nutri-ents (Figure 5.2). Cut each sample into three sectionsof equal length. Discard the bottom third; place the topone third in one paper bag and the middle one third inanother. Dry the samples in a warm room or oven.After drying, separate leaves from stems in middle onethird sample by rubbing the sample between yourhands. Put leaves and stems into separate bags. Figure5.2 and Table 5.4 list the analyses that should be per-formed on the samples. Table 5.6 lists guidelines forinterpreting plant tissue-test results. Entire plant sam-ples or baled hay samples are not recommendedbecause they can only detect extreme nutrient deficien-cies.

Tissue tests can determine only the single most lim-iting nutrient affecting plant growth—the concentra-tion of other nutrients may actually increase due toreduced growth. Therefore, correct the most severedeficiency first. After it is corrected, take new plant tis-sue samples to determine if other nutrients are defi-cient. Also, low concentrations of a nutrient in planttissue may not always indicate a deficiency in the soil.Remember that plant analysis reflects nutrient uptakeby the plant; a problem affecting roots, such as nema-todes, can affect nutrient uptake as well.

C O R R E C T I O N O F N U T R I E N T D E F I C I E N C I E S

Apply fertilizer to correct nutrient deficiencies aftercareful consideration of the amount of nutrientsremoved by alfalfa, the yield potential of the field, cur-rent soil-test levels, and historical responses to fertiliza-tion. Table 5.7 indicates the amount of nutrientsremoved by 4-, 6- and 8-ton alfalfa crops.

Nitrogen

Applying nitrogen fertilizer to alfalfa is seldombeneficial or profitable. Adequate nitrogen is providedby the symbiotic nitrogen-fixing bacteria (Rhizobia)that live in nodules on alfalfa roots. Symbiotic meansthat both the plant and bacteria benefit; the alfalfabenefits from the nitrogen provided by Rhizobia bac-teria and the bacteria benefit from the food source(carbohydrates) provided by alfalfa. Because of thisrelationship, applying nitrogen to alfalfa seldomresults in an economic yield response. In those rarecases where nitrogen fertilizer does result in a yieldincrease, the problem is probably ineffective inocula-tion or conditions that inhibit or retard the develop-

ment of the Rhizobia bacteria (that is, low soil pH,waterlogged soils, cold conditions, compacted soil, orextremely shallow root zone). Molybdenum andcobalt deficiencies are other possibilities.

Symptoms of nitrogen deficiency include stuntedgrowth and a light green or yellow color. A nitrogendeficiency is suspected when the field contains stuntedor small yellow plants with scattered tall dark greeninoculated plants (color photos 5.2 and 5.3). Exam-ination of roots usually shows no nodules on thestunted yellow plants and several nodules on the greenhealthy plants. Poor nodulation is often associatedwith fields having no history of alfalfa production; useof outdated inoculant; or hot, dry seedbed conditions.

The most common cause of nitrogen deficiency ispoor inoculation and nodule formation after planting.Proper inoculation is necessary to ensure that alfalfahas an adequate supply of nitrogen. For effective


Plant tissue tests can onlydetermine the most limiting nutrient for plant growth.


Figure 5.2. Plant tissue sampling and testing: (A) Collect 40 to 60 stems including leavesfrom at least 30 plants. (B) Cut stems into three sections of equal length. (C) Discard thebottom third. Place the top third in one paper bag and the middle third in another. Dry thesamples. Separate leaves from stems in middle third by rubbing between hands. Put leaves inone bag and stems in another bag. Analyze top-third sample for boron, molybdenum, andcopper. Analyze leaves from the middle third for sulfur (SO4–S) and the stems from middlethird for phosphorus (PO4–P) and potassium.

Table 5.6. Interpretation of test results for alfalfa plant tissue samples taken at 1⁄10 bloom.1

P L A N T T I S S U E VA LU E 2

N U T R I E N T P L A N T PA RT U N I T D E F I C I E N T M A RG I N A L A D E QUAT E H I G H

Sulfur (SO4–S) Middle third, leaves ppm 0–400 400–800 800–1000 Over 1000

Phosphorus (PO4–P) Middle third, stems ppm 300–500 500–800 800–1500 Over 1500

Potassium Middle third, stems % 0.40–0.65 0.65–0.80 0.80–1.5 Over 1.5

Boron Top third ppm Under 15 15–20 20–40 Over 200 3

Molybdenum Top third ppm Under 0.3 0.3–1.0 1–5 5–10 4

1. Concentrations should be higher if alfalfa is cut at bud stage (multiply tabular values by 1.10).2. An economic yield response to fertilizer applications is very likely for values below the deficient level,

somewhat likely for values in the marginal level, and unlikely for values over the adequate level.3. A concentration over 200 may cause reduced growth and vigor.4. A concentration over 10 may cause molybdenosis in ruminants.

Table 5.5. Interpretation of soil test results for alfalfa production.

S O I L VA LU E ( P P M ) 1

N U T R I E N T E X T R A C T 2 D E F I C I E N T M A RG I N A L A D E QUAT E H I G H

Phosphorus Bicarbonate < 5 5–10 10–20 >20

Potassium Ammonium acetate < 40 40–80 80–1253 >125

Sulfuric acid < 300 300–500 500–800 > 800

Boron Saturated paste < 0.14 0.1–0 .2 0.2–0 .4 >0.45

1. An economic yield response to fertilizer applications is very likely for values below the deficient level,somewhat likely for values in the marginal level, and unlikely for values over the adequate level.

2. Soil test values are based on use of the cited extract; values for other extracts are different.3. If ammonium acetate levels are <100 ppm, it is advisable to request sulfuric acid extractable K.4. Soil testing is not a suitable method to diagnose a deficiency. Use a plant tissue test.5. Possible toxicity to sensitive crops such as cereals.

A. Collect

B. Cut

C. Analyze

BoronMolybdenumCopper

PhosphorusPotassium

Sulfur

Discard

nodulation, inoculate seed with fresh inoculant and donot expose it to hot, dry conditions prior to germina-tion. This is particularly critical in fields planted to afirst crop of alfalfa. Fields with a history of alfalfa plant-ings seldom have inoculation problems, because of highresidual Rhizobia populations from previous crops. Ifpoor nodulation occurs in a young stand of alfalfa,inoculate seed at 2 to 5 times the normal rate and drill it into the stand at 3 to 5 pounds seed per acre. Followwith a light irrigation. Usually, after a growing season,all plants in the field will be inoculated.

Light green or yellow plants may also indicate a sul-fur or molybdenum deficiency. Use a plant tissue testto identify the specific deficiency. Nitrogen deficiencymay also result from a molybdenum deficiency, sincemolybdenum has a role in nitrogen fixation. Sulfurand molybdenum deficiencies will be discussed later in this chapter.

Phosphorus

Currently, phosphorus may be the most commonlydeficient nutrient in alfalfa in the IntermountainRegion. Prior to planting, use a soil test to assess thephosphorus status of the soil. As indicated in Table 5.5,soil with a phosphorus level less than 5 parts per mil-lion (ppm) is considered deficient, soil with 5 to 10ppm phosphorus is marginal, and that with 10 ppm orgreater phosphorus is adequate. A tissue test for phos-phorus is preferred after alfalfa is established.

Phosphorus deficiency is very difficult to identify visu-ally (color photo 5.1).

To correct a phosphorus deficiency, a high-analysisphosphorus fertilizer such as 0–45–0 or 11–52–0 isusually the most economical. In alfalfa these two com-

mon phosphorus sources result in the same yieldresponse. Liquid or granular phosphorus fertilizerswith water solubility values greater than 55 percent arenearly equal in terms of plant availability. Rock phos-phate, however, is not recommended because of lowphosphate availability, particularly when applied toanything other than very acidic soils (those with a pHless than 5.5). If before planting you use a nitrogen-phosphorus fertilizer such as 16–20–0 to stimulateyoung seedlings, take care to control weeds; the sup-plemental nitrogen will stimulate their growth.

Before planting, use soil tests to determine theamount of phosphorus needed (Table 5.8). Recent


Currently, phosphorus may bethe most commonly deficient

nutrient in alfalfa in theIntermountain Region.

Table 5.7. Nutrients contained in 4, 6, and 8 tons of alfalfa hay.1

N U T R I E N T Y I E L D ( L B / A )

N U T R I E N T S Y M B O L 4 – TO N C RO P 6 – TO N C RO P 8 – TO N C RO P

Nitrogen N 200.0 300.0 400.0

Phosphorus P2O5 48.0 71.0 95.0

Potassium K2O 173.0 260.0 346.0

Calcium Ca 128.0 192.0 256.0

Magnesium Mg 27.0 40.0 53.0

Sulfur S 16.0 24.0 32.0

Iron Fe 1.5 2.3 3.0

Manganese Mn 1.0 1.5 2.0

Chlorine Cl 1.0 1.5 2.0

Boron B 0.2 0.4 0.5

Zinc Zn 0.2 0.3 0.4

Copper Cu 0.06 0.1 0.13

Molybdenum Mo 0.008 0.012 0.016

1. 100% dry matter

research indicates that even if high rates of phosphorusare applied, it may be economical to reapply after 2years. Incorporate no more than a 2-year supply of fer-tilizer into the top 2 to 4 inches of soil. Use tissueanalysis to determine the need for phosphorus after theseedling year. Applying phosphorus fertilizers on thesoil surface in an established stand has been very effec-tive. Apply fertilizer any time, but applications madefrom October through February are preferred becausealfalfa responses to phosphorus fertilizer are not usual-ly observed until 60 to 90 days after application.

Table 5.8 gives a range of application rates becausesome soils and growing conditions require largeramounts to meet nutrition requirements and maintainhigh alfalfa yields. Various combinations of phospho-rus amounts and application timing can be used toachieve the rates recommended. Recent research hasindicated that fewer applications (at least every 2years) of higher rates can be applied more economical-ly than lower rates (less than 50 pounds P2O5 peracre) applied each year. Take plant tissue samples 60 to 90 days after a fertilizer application to re-evaluatefertility status.

Potassium

Potassium deficiency is found less frequently in theIntermountain Region of northern California. Like alack of phosphorus, a potassium deficiency can be diag-nosed by either a soil or a plant tissue test. The visualsymptoms of potassium deficiency are pinhead-sizedwhite or yellow spots on new leaves (see color photo5.6). Unlike the symptoms of other nutrient shortages,those of potassium deficiency are distinctive and fairlyreliable. Note, however, that genetic differencesbetween alfalfa plants affect symptom development;

not all potassium-deficient plants show deficiencysymptoms. Also, some insects and diseases cause symp-toms similar to those of potassium deficiency.

The most economical fertilizer for correcting thisdeficiency is muriate of potash (0–0–60). Sometimespotassium sulfate (0–0–52, 18% sulfur) is used whensulfur is also deficient. However, compared to muriateof potash, potassium sulfate and other mixed fertilizersare usually more expensive per pound of potassium.Table 5.8 lists recommended potassium rates for bothpreplanting and surface applications. Applications onthe soil surface are very effective and can be made any-time. Like the response to phosphorus, the growthresponse to applied potassium may not be observeduntil 60 to 90 days after fertilizer application.

Sulfur

Historically, sulfur has been the most commonlydeficient nutrient in alfalfa in the IntermountainRegion. Visual deficiency symptoms include stuntingand a light green or yellow color—symptoms that mayalso indicate nitrogen or molybdenum deficiency (seecolor photos 5.2 and 5.4). Only tissue testing canconfirm a sulfur deficiency; soil tests do not providereliable results. It is important to have an adequatelevel of available sulfate sulfur in the soil at the time ofplanting. Two principal sources of sulfur exist: (1)long-term slowly available elemental sulfur and (2)short-term rapidly available sulfate. The most eco-nomical practice is to apply and incorporate beforeplanting 200 to 300 pounds elemental sulfur per acre.Elemental sulfur is gradually converted to the sulfateform and should last 4 to 7 years. It may be necessaryto repeat the application once in the life of a 6- to 10-year stand.

Table 5.8. Recommended phosphorus and potassium application rates based on results of soil or plant tissue tests.

S O I L O R P L A N T T I S S U E T E S T R E S U LT

N U T R I E N T Y I E L D L E V E L D E F I C I E N T 1 M A RG I N A L A D E QUAT E

( TO N S / A ) ( L B / A ) ( L B / A ) ( L B / A )

Phosphorus (P2O5) 4 60–90 30–45 0–20

8 120–180 60–90 0–45

Potassium (K2O) 4 100–200 50–100 0–50

8 300–400 150–200 0–100

1. An economic yield response to fertilizer applications is very likely for values below the deficient level, somewhat likely for values in the marginal level, and unlikely for values over the adequate level.


To ensure a multiple-year supply of available sulfur,the particle size of elemental sulfur must range fromlarge to small. Small particles are rapidly converted tothe sulfate form; the large particles will continue torelease sulfate over several years. Ideally, 10 percent ofelemental sulfur should pass through a 100-meshscreen; 30 percent, through a 50-mesh screen; and theremaining 60 percent, through a 6-mesh screen. Veryfine grades of sulfur are readily available but do notpersist long enough to provide a multiple-year supply.

Fertilizers used to supply the sulfate form of sulfurinclude gypsum (15 to 17% sulfur), 16–20–0 (14 to15% sulfur), and ammonium sulfate 21–0–0 (24%sulfur). Some growers apply 300 to 500 pounds gyp-sum per acre every other year rather than using ele-mental sulfur. The advantage to this practice is a quickresponse (about 2 weeks). The disadvantages are thehigher cost per pound of sulfur and the fact that moresulfur is applied than is necessary. Perhaps the mostimportant reason to avoid overfertilization with sulfuris that it can decrease the selenium concentration inthe alfalfa hay. Livestock producers throughout theIntermountain Region want forage that is as high inselenium as possible because their animals often sufferfrom selenium deficiency.

Iron

On rare occasion, growers have observed symptoms of iron deficiency in alfalfa, but only tissue tests havebeen effective in confirming the problem. Thedeficiency usually produces nearly white or canary yellow plants in areas where drainage is poor. Irondeficiency in alfalfa is characteristically associated withhigh pH or poorly drained soils high in lime. If the soilpH is greater than 8.0 and free lime is present, begin tocorrect the iron deficiency by applying high rates ofelemental sulfur (at least 1,000 pounds per acre); thiswill lower the soil pH. Also, improve drainage in lowareas of the field.

Boron

Although deficiency symptoms are easily identified,boron deficiency is more effectively confirmed with a

plant tissue test (color photo 5.7). Adequate supplies ofboron are more important for production of alfalfa seedthan hay. When tissue tests indicate boron is deficientand boron-sensitive crops such as cereals are likely to beplanted in the field within 12 months, apply 1 to 3pounds boron per acre to the soil surface. Use 3.5 to 7pounds per acre if boron-tolerant crops such as alfalfa,sugarbeets, or onions will be grown for the next 24months. Use the lower rates on sandy soils; the higherrates are suggested for fine-textured soils. Higher ratesof boron will often last 5 to 7 years. The most commonboron fertilizers are 45 to 48 percent borate (14.3 to14.9% boron) and 65 to 68 percent borate (20.4 to21.1% boron). Boron is usually applied as a granularproduct, either by air or through the small seed box in agrain drill. Some forms can be applied as a liquid alongwith herbicide applications; make sure the boron andherbicide are compatible before mixing them.

Molybdenum

Molybdenum deficiency is infrequent in theIntermountain Region, but it has occurred in severalareas. Symptoms of molybdenum deficiency are likethose of nitrogen and sulfur deficiency: light green oryellow stunted plants (color photo 5.5). A positiveresponse to ammonium sulfate fertilizer could mean anitrogen, sulfur, or molybdenum deficiency. A positiveresponse to urea rules out a sulfur deficiency but couldindicate a shortage of nitrogen or molybdenum. Planttissue testing or applying sulfur and molybdenum fer-tilizers to separate trial strips are the only means ofconfirming a molybdenum deficiency.

The most common molybdenum fertilizer is sodiummolybdate (40% molybdenum), but ammoniummolybdate can be used as well. Apply 0.4 pound molyb-denum per acre during the winter or before regrowthhas occurred after cutting. A single application ofmolybdenum should last from 5 to 15 years. Thoroughrecords of molybdenum application times and amountsalong with repeated tissue testing are essential to deter-mine when to apply or reapply the nutrient.

Do not apply excessive molybdenum (that is, dou-ble or triple coverage)—the concentration of the ele-ment in alfalfa may become so high that the foragebecomes toxic to livestock. For the same reason, do not


apply molybdenum to foliage. Analyzing the top thirdof the plant for both copper and molybdenum candetect deficiencies and suboptimum ratios of these ele-ments. Consult a nutrition specialist if you suspectmolybdenum problems.

R E C O R D K E E P I N G

Clear and complete records are essential to a successfulalfalfa fertility program. Keep a record for each fieldand include the location of permanent benchmarkareas, dates of sampling, soil and plant tissue testresults, fertilizer application dates, fertilizers appliedand the rate of application, and crop yields. This infor-mation can help you evaluate both the need for and theresponse to applied fertilizer and allow you to developan economical, long-term fertilization program.


DANR Analytical Lab. 1991. California commercial laboratoriesproviding agricultural testing. Oakland: University of CaliforniaDivision of Agriculture and Natural Resources, SpecialPublication 3024.

Kelling, K. A., and J. E. Matocha. 1990. Plant analysis as an aid infertilizing forage crops. In R. L. Westerman, (ed.), Soil testingand plant analysis, third edition, 603–43. Madison, WI: SoilScience Society of America.

Martin, W. E., and J. E. Matocha. 1973. Plant analysis as an aid inthe fertilization of forage crops. In L. M Walsh,. and J. D.Beaton (eds.), Soil testing and plant analysis, revised edition,393–426. Madison, WI: Soil Science Society of America.

Meyer, R. D., and W. E. Martin. 1983. Plant analysis as a guidefor fertilization of alfalfa. In H. M. Reisenauer, (ed.), Soil andplant tissue testing in California, 32-33. Oakland: University ofCalifornia Division of Agriculture and Natural Resources,Bulletin 1879.

Reisenauer, H. M., J. Quick, R. E. Voss, and A. L. Brown. 1983.Chemical soil tests for soil fertility evaluation. In H. M.Reisenauer, (ed.), Soil and plant tissue testing in California,39–41. Oakland: University of California Division ofAgriculture and Natural Resources, Bulletin 1879.

Soil Improvement Committee, California Fertilizer Association.1985. Western fertilizer handbook, 7th edition. Danville, IL:The Interstate Printers and Publishers.


51

C H A P T E R S I X

W E E D SJerry L. Schmierer and Steve B. Orloff

�eeds compete with alfalfa for water,nutrients, light, and space. If weeds areleft uncontrolled, they can reduce alfal-

fa yields and weaken or even destroy the stand. Weedsalso reduce the quality and value of alfalfa hay becausemost weeds are less palatable and less nutritious thanalfalfa. Some weeds—such as hare barley (commonlycalled foxtail), downy brome (cheatgrass), and greenfoxtail (bristlegrass)—can injure the mouths of live-stock, rendering the forage less palatable. Others, suchas fiddleneck and yellow starthistle, are poisonousand, if present in sufficient quantities, make the forageunsuitable for livestock consumption.

Weed control can be particularly challenging in theIntermountain Region because of long alfalfa standlife. Weeds invade the open areas that often occur inolder depleted alfalfa stands. Weed control is prob-lematic when fields remain in the same crop for manyyears and where few rotation crops are grown, twoconditions that are common in many parts of theIntermountain Region.

W E E D B I O L O G Y

Effective weed management requires an understand-ing of weed biology. Weeds are classified according totheir life cycle and fall into three groups: annuals,biennials, and perennials. Table 6.1 lists commonweeds that occur in intermountain alfalfa fields.

Annual weeds emerge from seed, grow, flower, pro-duce seed, and die within a year. Plants the next sea-son must emerge from seed. Annual weeds are dividedinto winter and summer annual weeds, depending ongrowth pattern. Winter annual weeds germinate in thefall through early spring (October to March), whensoil temperature and moisture are favorable. Theygrow rapidly in the spring and are usually a problemonly in the first cutting of alfalfa. Summer annualweeds germinate as temperatures rise in the late spring(April to May) through summer, whenever soil mois-ture is adequate. Summer annual weeds are not aproblem in the first cutting of established stands, butthey appear in the second and later alfalfa cuttings.Only a few weeds in alfalfa are classified as biennials,which require 14 to 24 months to complete their life


Table 6.1. Problem weeds of alfalfa in the Intermountain Region of California.

C O M M O N N A M E B OTA N I C A L N A M E FA M I LYW I N T E R A N N UA L W E E D S

Shepherdspurse Capsella bursa-pastoris Mustard

Flixweed Descurainia sophia Mustard

Tansymustard Descurainia pinnata Mustard

Tumble mustard/Jim Hill mustard Sisymbrium altissimum Mustard

Field pepperweed Lepidium campestre Mustard

Yellowflower pepperweed Lepidium perfoliatum Mustard

Prickly lettuce Lactuca serriola Lettuce

Downy brome (cheatgrass) Bromus tectorum Grass

Hare barley (foxtail) Hordeum leporinum Grass

Wild oats Avena fatua Grass

Volunteer cereals Grass

SUMMER ANNUAL BROADLEAF WEEDS

Pigweed Amaranthus spp. Amaranth

Lambsquarters Chenopodium album Goosefoot

Russian thistle Salsola iberica Goosefoot

Common sunflower Helianthus annuus Thistle

Dodder Cuscuta spp. Morningglory

Witchgrass Panicum capillare Grass

Green foxtail (bristlegrass) Setaria viridis Grass

Stinkgrass (lovegrass) Eragrostis cilianensis Grass

Barnyardgrass Echinochloa crus-galli Grass

Italian ryegrass Lolium multiflorum Grass

PERENNIAL AND BIENNIAL WEEDS

Swamp knotweed Polygonum coccineum Buckwheat

Chicory Cichorium intybus Thistle

Common dandelion Taraxacum officinale Thistle

Cheeseweed Malva spp. Mallow

Canada thistle Cirsium arvense Thistle

Bull thistle Cirsium lanceolatum Thistle

Poverty sumpweed Iva axillaris Thistle

Buckhorn plaintain Plantago lanceolata Plantain

Bulbous bluegrass Poa bulbosa Grass

Foxtail barley Hordeum jubatum Grass

Kentucky bluegrass Poa pratensis Grass

Squirreltail Sitanion hystrix Grass

Quackgrass Elytrigia repens Grass

Perennial ryegrass Lolium perenne Grass

Tall fescue Festuca spp. Grass

Muhly Muhlenbergia spp. Grass

Meadow foxtail Alopecurus pratensis Grass

w e e d s 53

cycle. In alfalfa, perennial weeds are much more com-mon than biennials. They live for 3 years or longer.Some perennials, such as dandelion and plantain,reproduce from seed. Others, such as field bindweed,quackgrass, and Canada thistle, are creeping perenni-als with vegetative structures (stolons or rhizomes)that permit them to produce asexually, without seed.

W E E D C O N T RO L

An integrated approach that employs cultural,mechanical, and chemical control is the most effectivemethod for controlling weeds in alfalfa. (Table 6.2gives an overview of herbicides registered for use inCalifornia alfalfa fields.) Controlling weeds in a thin,weak alfalfa stand is very difficult or even impossible.Agronomic practices that promote a dense vigorousstand of alfalfa are a primary component of any suc-cessful weed control program. These practices (whichinclude managment of planting date, fertilization,irrigation, and harvest) are explained in detail in otherchapters of this book.

Weed management in alfalfa involves two distinctphases: weed control in seedling alfalfa and weed con-

trol in established alfalfa. Control of perennial weedsoccurs in seedling alfalfa and established alfalfa; it willbe discussed last.

W E E D C O N T RO L I N S E E D L I N G A L FA L FA

Alfalfa is most vulnerable to weed competition whenit is in the seedling stage. Alfalfa seedlings grow slowlyand do not compete well with weeds, which are oftenmore vigorous. Aside from the poor quality of a weedyfirst cutting, weeds in seedling alfalfa can severelyreduce stand. In the absence of adequate control mea-sures, severe weed infestations can cause stand estab-lishment failures.

Cultural Control

Crop rotation can be effective for reducing weed pop-ulations in seedling alfalfa. Some weeds are more easi-ly controlled in other crops than they are in alfalfa.For example, relatively inexpensive phenoxy herbi-cides control most broadleaf weeds in grain. By con-

Table 6.2. Time of application and method of activity for herbicides used in alfalfa.

CROP STAGE TIME OF HERBICIDE APPLICATION HERBICIDE ACTIVITY

Seedling Established Before Weed After WeedHerbicide Alfalfa Alfalfa Preplant Emergence Emergence Soil Active Foliar Active

Eptam (EPTC) Yes Yes Yes Yes No Yes No

Balan (benefin) Yes No Yes Yes No Yes No

Butyrac, Butoxone (2,4-DB) Yes Yes No No Yes No Yes

Buctril (bromoxynil) Yes No No No Yes No Yes

Poast (sethoxydim) Yes Yes No No Yes No Yes

Kerb (pronamide) Yes Yes No Yes Yes Yes No

Gramoxone (paraquat) Yes Yes Yes No Yes No Yes

Velpar (hexazinone) Yes1 Yes No Yes Yes Yes Some

Karmex, Direx (diuron) No Yes No Yes Some Yes Slight

Lexone, Sencor (metribuzin) No Yes No Yes Yes Yes Some

Treflan (trifluralin) No Yes No Yes No Yes No

1. California registration only

trolling broadleaf weeds in a grain crop that precedesalfalfa, the weed infestation in a seedling alfalfa field islessened. Similarly, weed infestations are generally lowfollowing high-value row crops which are often main-tained nearly weed-free.

Further reduce weed problems in alfalfa by plant-ing when weed populations are low and growing con-ditions are optimal for alfalfa. Low temperatures favorthe growth of winter annual weeds over alfalfa; hightemperatures favor summer annual weed growth. Awindow of opportunity for planting occurs in latesummer. This is the time when summer annual weedsdecline in number and vigor and before most winterannual weeds emerge. Summer annual weeds thatemerge in the late summer go into a reproductivestage sooner than summer annual weeds that emergein spring. During this stage the weeds compete lessthan usual with alfalfa. Summer annual weeds thatemerge with the crop are subsequently killed by fallfrosts. Therefore, plant during this window, whenmoderate temperatures favor alfalfa growth over theweeds. A similar window occurs in the spring, aftermost of the winter annual weeds have emerged butbefore summer annual weeds become troublesome.

Weed problems can be reduced by preirrigating andthen cultivating with a harrow or disc after weedemergence. This does not completely eliminate weeds,but it reduces their population and makes other con-trol measures more effective.

Healthy alfalfa is an excellent competitor withweeds. Therefore, a key to effective weed managementis to maintain a dense, vigorous stand of alfalfa. Selectan adapted alfalfa variety, and plant weed-free certifiedalfalfa seed. An adequate seeding rate and properseedbed preparation help ensure a dense stand (seechapter 2). High alfalfa seeding rates enhance thecompetitiveness of alfalfa, but an excessive seeding rateis an expensive weed control method. Proper fertility

is also important in maximizing the competitivenessof seedling alfalfa.

Small-grain companion crops are sometimes used forweed control in seedling alfalfa. A companion cropreplaces undesirable weedy species and is itself a desir-able forage that, the grower hopes, is not too competi-tive. To avoid excessive competition with alfalfa,companion crop seeding rates should not exceed 20pounds per acre. Such a low seeding rate can usuallyonly suppress weeds, not provide complete control. (Seechapter 2 for more information on companion crops.)

Early mowing or clipping can be an effective way torescue an alfalfa planting that is heavily infested withweeds. Mowing tall weeds improves sunlight penetra-tion into the canopy. Many weeds do not recover aftercutting, which allows alfalfa to compete more success-fully. Also, weeds are more palatable and nutritiouswhen cut early. However, if some weed species, espe-cially grasses, are cut too early (for example, prior tobloom), they recover after mowing and contaminatesubsequent cuttings. Realize that early mowingdepletes stored carbohydrate root reserves, reducingthe vigor of alfalfa. So mow early only when weeds areovertopping and shading the alfalfa. After cuttingearly, lengthen the time interval between the first andsecond cuttings. This will allow sufficient time forroot reserves to be replenished.


Alfalfa is most vulnerable to weed competition when it

is in the seedling stage.

Table 6.3. Application times for herbicides registered for use inseedling alfalfa fields.

TIME OF APPLICATION HERBICIDE

Preplant Roundup (glyphosate)

Postemergence to weed Gramoxone (paraquat)

Preplant Balan (benefin)

Pre-emergence to weed Eptam (EPTC)

Mixture of Balan and Eptam

Postplant Buctril (bromoxynil)

Postemergence to weed Butyrac, Butoxone (2,4-DB)

and alfalfa Kerb (pronamide)

Poast (sethoxydim)

Gramoxone (paraquat)1

Postplant Velpar (hexazinone)

Newly established alfalfa Gramoxone (paraquat)

1. Apply at a low rate; follow manufacturer’s instructions.

Chemical Control

Cultural control practices alone are often insufficient toadequately control weeds in seedling alfalfa; they mustbe supplemented with herbicides. Several herbicides areregistered for use in seedling alfalfa fields (Table 6.3).No single herbicide used in seedling alfalfa will controlthe entire spectrum of weeds in intermountain alfalfafields (Table 6.4). Therefore, weed identification is fun-damental to proper herbicide selection. Weeds of the

West (listed under Additional Reading at the end of thischapter) is an excellent weed identification reference.

Preplant foliar herbicidesNonselective herbicides can control emerged weedsprior to the planting of alfalfa. Both glyphosate(Roundup) and paraquat (Gramoxone) are registeredfor this use. These herbicides control emerged weedsonly; they do not control weeds that emerge afterapplication. Preplant foliar herbicides are most effec-

w e e d s 55

Table 6.4. Weed susceptibility to herbicides registered for use on seedling alfalfa1

P R E P L A N T P O S T E M E RG E N C E

B A L A N E P TA M B U C T R I L 2 , 4 - D B K E R B P OA S T G R A M OX O N E

WINTER ANNUAL WEEDS

Downy brome (cheatgrass) P C N N C P-C C

Hare barley (foxtail) P P N N C P-C C

Volunteer cereals P C N N C C P-C

Fiddleneck C P C N-P N N P-C

Flixweed N N P C N N C

Tumble mustard N N C C N N P

Shepherdspurse N P C C N N P

Prickly lettuce N C P-C C N N C

Clasping pepperweed – – C C N N C

Filaree C C N C P N P

SUMMER ANNUAL WEEDS

Barnyardgrass C C N N N C P

Green/yellow foxtail C C N N P C C

Lovegrass C C N N C C C

Witchgrass C C N N C C C

Lambsquarters C C C C N N P-C

Nightshade N C C C N N C

Pigweed C C P C N N P-C

Russian thistle P P C P P N P

Knotweed C P P P N-C N P

Dodder N N N N P N P

PERENNIAL WEEDS

Bulbous bluegrass – – N N C – C

Foxtail barley P P N N C P P

Kentucky bluegrass – – N N C P P

Quackgrass – P N N C P N

Field bindweed N N N N-P – N N

Dandelion – – N CSO N N P

Plantain – – N CSO N N –

N = no control; P = partial control; C = control; – = no information available; CSO = control of seedling weeds only1. Weed susceptibility to Velpar is found in Table 6.5.

tive for early spring plantings where the seedbed is pre-pared in the fall and weeds emerge with winter rains.The field is treated, and then the alfalfa is drilled witha no-till or conventional drill, without disturbing thesoil. Soil disturbance brings weed seeds to the surface,reducing the effectiveness of this treatment.

Preplant soil herbicidese p t c ( e p ta m ) a n d b e n e f i n ( b a l a n )These herbicides are used before planting and priorto weed and crop emergence. Do not use them whena small-grain companion crop is planted; it will bekilled. Eptam and Balan are generally applied to thesoil surface and mechanically incorporated into thesoil. Eptam can also be injected into irrigation water.These herbicides are often applied and incorporatedin the same pass. To minimize volatilization losses,avoid spraying Eptam onto moist soil. Herbicides canbe incorporated with a power-driven rotary tiller orby discing twice, at right angles. Set power-driventillers to the desired depth of incorporation; set discsor ground-driven tillers to twice as deep as thedesired incorporation depth. For most annual weeds,incorporation depth should be 1 to 2 inches. When

using Eptam to control volunteer cereals, quackgrass,and wild oats, incorporation depth should be 2 to 3inches. Balan is more expensive but more persistentthan Eptam—the soil life of Balan is 3 to 5 months;that of Eptam is 1 to 2 months. Alfalfa is seldominjured from applications of Balan, but Eptam hascaused stunted plants with malformed (cupped andclasped) leaves (color photo 6.1). However, cropinjury is usually confined to alfalfa grown in coarse-textured soils, and symptoms are usually temporary.Postemergence applications of 2,4-DB following pre-plant Eptam applications can cause excessive injurybecause Eptam reduces the protective cuticle layer of

alfalfa, allowing it to absorb more 2,4-DB than itwould otherwise.

Eptam and Balan are more suited to a spring plant-ing than a late summer or fall planting. They control abroad spectrum of summer annual weeds but do notcontrol many of the problem winter annual weeds,such as those in the mustard family. Results have beensomewhat erratic in the Intermountain Region, evenon spring plantings. This may be due to inadequateincorporation procedures. Eptam and Balan can betank-mixed at lower rates of each to expand the spec-trum of weeds controlled. Consult manufacturer’sinstructions before mixing.

Postemergence herbicidesPostemergence herbicides are often used in preferenceto preplant herbicides because they allow the grower toevaluate the weed pressure, identify weed species priorto application, and select an herbicide according to itseffectiveness on the weed species present. Proper appli-cation timing is critical because small weeds are mucheasier to control than large ones. Late application is themost common reason for postemergence herbicide fail-ure. In general, apply postemergence herbicides whenalfalfa reaches the minimum growth stage stated on theherbicide label. Figure 2.4 shows seedling alfalfa growthstages. Remember, that a true alfalfa leaf is trifoliolate(it has three leaflets attached to a single petiole); do notconfuse cotyledons or unifoliolate leaves with trueleaves, or you may apply the herbicide too soon.

2 , 4 - d b ⁽ b u t y r a c , b u t ox o n e ⁾ The herbicide2,4-DB is very effective at controlling many of thebroadleaf weeds that emerge with alfalfa in bothspring and late summer or fall plantings. Only theamine formulation of 2,4-DB is currently available,and its performance is inferior to that of the ester for-mulation, which was used formerly. Research hasindicated that the activity of 2,4-DB amine can beimproved to a level comparable to that of the esterformulation by adding a nonionic surfactant at 0.25percent (one quart per 100 gallons spray volume).Young, vigorously growing weeds are most suscepti-ble. Apply when alfalfa has two to four trifoliolateleaves. The best control is obtained when several daysof warm sunny weather follow 2,4-DB applications.Apply as soon as possible after an irrigation or rain-fall. Irrigation or significant rainfall within 3 to 5days after application can cause alfalfa injury (color


Late application is the most common reason

for postemergence herbicide failure.

photo 6.2). Because of rain, spring applications of2,4-DB can be difficult to accomplish in theIntermountain Region.

b r o m ox y n i l ⁽ b u c t r i l ⁾ Like 2,4-DB, Buctrilis used for broadleaf weed control in seedling alfalfa.Alfalfa must have a minimum of four trifoliolateleaves before it can be treated safely with Buctril.Weed size is critical when using this chemical. Besure weeds are not taller than 3 inches and do notexceed the four-leaf stage. Do not apply when tem-peratures may exceed 80oF (27oC) during or follow-ing application; Buctril may injure alfalfa if the tem-perature is too high (color photo 6.3). Excessiveinjury can also occur in the Intermountain Regionwhen an application follows a period of cool, overcastweather. For these reasons, applying Buctril in springor summer can be difficult. A drawback of Buctril isthat it does not completely control pigweed (especial-ly if it is taller than 2 to 3 inches), a common sum-mer annual weed in spring- and summer-plantedalfalfa. However, it is more effective than 2,4-DB forfiddleneck and Russian thistle control. Combinationsof Buctril and 2,4-DB can be effective for controllinga broader spectrum of weeds than either herbicidecan control when used alone.

s e t h ox y d i m ⁽ p o a s t ⁾ This chemical controlsemerged grasses selectively, with no injury to seedlingalfalfa or broadleaf weeds. Poast can be applied safelyat any alfalfa growth stage; however, treatment ispreferable when grasses are small, before the alfalfacanopy covers grass seedlings. For best results, applyPoast when grasses are growing vigorously, not whenthey are moisture-stressed. In addition to weedygrasses, Poast can control dense stands of volunteercereals or an aggressive companion crop. Poast hasnot been widely used in the Intermountain Region,because problems with grass are not common inspring-planted seedling alfalfa. Hare barley (foxtail)and downy brome (cheatgrass) may appear in fall-planted fields, but under most conditions Poast provides only partial control of these weeds. (Theproduct Poast Plus controls these weeds, but is notcurrently registered in California.) Poast will not con-trol bluegrass species.

p r o n a m i d e ⁽ k e r b ⁾ Used in seedling alfalfa tocontrol winter annual grasses and volunteer cereals,

Kerb is active in soil. It provides both pre-emergenceand postemergence control of susceptible weeds. Kerbcontrols certain broadleaf weeds at high applicationrates, but not at the low rates used in alfalfa. (Higherrates are generally not cost-effective.) Inconsistent orincomplete weed control may occur in soils contain-ing more than 4 percent organic matter. Kerb is safefor use on seedling alfalfa and may be applied to alfal-fa with one to four trifoliolate leaves. Approximately 1⁄2inch of rainfall or overhead irrigation is required afterapplication to move the herbicide into the root zone.Greater quantities of water may wash Kerb too deepinto the soil, resulting in poor weed control. The timespan between application and incorporation is not ascritical in cool temperatures (those below 55oF, or13oC) as in warm temperatures. Kerb acts slowly,requiring as long as 60 days from the time of incorpo-ration to kill many grasses. If a Kerb-treated fieldneeds to be replanted, residual herbicide can injureemerging alfalfa seedlings.

pa r a q u at ⁽ g r a m ox o n e ⁾ Do not applyGramoxone to alfalfa with fewer than three trifoliolateleaves. As the manufacturer’s label warns, stands willbe reduced by application when alfalfa is too young;reduction can be so severe that replanting is necessary.The rate and safety of Gramoxone use increase whenalfalfa reaches the six-trifoliolate leaf stage and againwhen the plant reaches the nine-trifoliolate-leaf stage.Alfalfa foliage present at the time of application willbe burned; compared to young plants, more maturealfalfa is better able to withstand the injury. Do notuse Gramoxone on a spring planting, because it doesnot control some of the common summer annualweeds (such as lambsquarters and pigweed) andbecause crop injury is likely. The best use forGramoxone is on newly established alfalfa during thefirst dormant season after planting.

h e x a z i n o n e ⁽ v e l pa r ⁾ Like Gramoxone,Velpar can be used for weed control in seedling alfal-fa, though crop safety is marginal. The advantages ofVelpar are that it controls a broad spectrum of grassand broadleaf weeds and it is less expensive than mostother herbicides for seedling alfalfa. Apply Velpar onlyto alfalfa plants that have lateral secondary growthand roots longer than 6 inches. Applications can bemade only in the winter months, when alfalfa plantsare not actively growing. Therefore, the use of Velpar

w e e d s 57

on first-year alfalfa in the Intermountain Region isrestricted to dormant applications with low rates tonewly established alfalfa planted by mid-August.

i m a z e t h a p y r ⁽ p u r s u i t ⁾ At the time of publi-cation, January 1995, Pursuit is not registered inCalifornia. Pursuit, a postemergence herbicide, hasbeen evaluated in field trials in the IntermountainRegion and throughout California. It controls mostof the winter and summer annual weeds encounteredin intermountain seedling alfalfa fields, includingfilaree, pigweed, nightshade, and weeds in the mus-tard family (such as tansymustard, flixweed, tumblemustard, and shepherdspurse). It suppresses manygrasses and therefore should not be applied when acereal is planted as a companion crop to alfalfa. Onlya few common broadleaf weeds escape control.Pursuit only stunts Russian thistle and lambsquarters,unless it is applied when these weeds are very small.This herbicide cannot control prickly lettuce andannual sowthistle. Pursuit is slow acting, especiallywhen temperatures are cool. Susceptible weeds stopgrowing soon after application; they die within a fewweeks. Pursuit has tremendous potential for weedcontrol in seedling alfalfa fields; however, do not con-sider using this herbicide until it receives Californiaregistration.

W E E D C O N T RO L I NE S TA B L I S H E D A L FA L FA

Weed management in established alfalfa can be divid-ed into three categories: control of winter annualweeds, control of summer annual weeds, and controlof perennial weeds.

Winter Annual Weed Control

Winter annual weeds emerge with fall and winter rain.Winter weather kills some species, but enough weedsusually either survive or emerge late to infest the firstcutting of alfalfa and contaminate the hay. Culturalcontrols are largely ineffective, because alfalfa does notcompete well with weeds that emerge before the cropbreaks dormancy.

Light cultivation with a harrow (a spring-toothed

harrow, spike-toothed harrow, or Danish tine harrow)to uproot winter annual weeds can be partially effec-tive under some circumstances. Timing is critical. Thefield must be harrowed after most of the weeds haveemerged but just prior to the time alfalfa breaks dor-mancy and resumes growth. If fields are cultivated tooearly, subsequent rains can germinate a new crop ofweeds. Injury to alfalfa crown buds and regrowthincrease when the field is harrowed too late. Damageto crowns increases their susceptibility to disease.Fields heavily infested with weeds can be mowed early,but with the same drawbacks discussed earlier (in thesection on weed control in seedling alfalfa).

Herbicides are usually required for complete controlof winter annual weeds. The herbicides diuron(Karmex or Direx), hexazinone (Velpar), metribuzin(Sencor or Lexone), and Gramoxone are registered foruse in established alfalfa. Effective weed control pro-grams for the Intermountain Region may use theseherbicides alone or in combination. Factors to consid-er when selecting the proper herbicide or herbicidecombination include the following:

• weed history• soil texture• soil organic matter• likelihood of rainfall for incorporation of herbicides• remaining stand life (Will the field be taken out of

production after the current production season?)• economics

These factors will be discussed later in this chapter inrelation to specific herbicides.

Soil-active herbicidesv e l pa r , k a r m e x , a n d s e n c o r These threechemicals control a broad range of annual and peren-nial weeds (Table 6.5). These herbicides are soil activeand inhibit photosynthesis in susceptible plants.Alfalfa must be established for at least one year beforeKarmex or Sencor can be applied. If alfalfa is not dor-


Herbicides are usuallyrequired for complete control

of winter annual weeds.

mant significant injury can occur (color photo 6.4).Soil-active herbicides must be incorporated into thesoil by rainfall or sprinkler irrigation.

Velpar controls most winter annual weeds and sup-presses many perennial weeds that infest intermoun-tain alfalfa fields. In fact, of the soil-applied herbicides,Velpar has the broadest spectrum of activity. Its activ-ity is similar to that of Sencor, but Velpar is more effec-tive at controlling shepherdspurse, one of the mostcommon weeds infesting alfalfa (Figure 6.1). It is eveneffective on soils high in organic matter, such as thosein the Tulelake Basin. Velpar is more effective onemerged weeds than other soil-active herbicides, par-ticularly when a nonionic surfactant is added. How-ever, do not add surfactant after alfalfa growth begins,or significant crop injury may result. Use rates varyaccording to weed species and soil types; refer to herbi-cide labels for specific rate recommendations. Reducedrates of Velpar (such as 0.375 pound active ingredientper acre on sandy loam soil low in organic matter)have been used successfully where Velpar is used 2 ormore years in succession. Velpar is persistent in soil.Do not plant other crops for at least two years follow-ing an application of Velpar.

Karmex, also sold as Direx, controls a broad spec-trum of winter annual weeds in alfalfa. It is less expen-sive than Velpar but less effective on emerged weeds,particularly emerged grasses such as downy brome(cheatgrass). If the population of emerged weeds islarge, tank-mix Karmex with Velpar or Gramoxone forimproved control. (Karmex is frequently tank-mixedwith Velpar at reduced rates of each. This broadens theweed spectrum controlled and reduces cost.) Do notapply Karmex to sandy soil.

The activity of Sencor, also sold as Lexone, is similarto that of Velpar. It is commonly used in the last yearof production of an alfalfa field, especially in fieldswhere potatoes follow alfalfa. In addition to beinglabeled for use on alfalfa, Sencor is labeled for use onmixed stands of alfalfa and grasses. Low rates can beused to control weeds and to prevent excessive compe-tition from grasses.

Foliar herbicidesg r a m ox o n e a n d 2 , 4 - ð b These two foliar her-bicides are registered for use in established alfalfa. Theherbicide 2,4-DB is comparatively expensive and con-trols only small broadleaf weeds. Alfalfa injury from2,4-DB is more prevalent in established than in

seedling alfalfa. Therefore, in the IntermountainRegion, limit its use to seedling alfalfa.

Gramoxone controls a range of winter annual weeds(Table 6.5) and is widely used in the IntermountainRegion. Because Gramoxone is inactive in soil, it iswell suited for use in the last year of an alfalfa stand. Itis especially effective on winter annual grasses such ashare barley (foxtail) or downy brome (cheatgrass).Small, vigorously growing weeds are most susceptible,

w e e d s 59

Figure 6.1. (A)Shepherdspurseand (B) tansy-mustard are themost commonwinter annualweeds found inintermountainalfalfa fields.

(A)

(B)


Table 6.5. Weed susceptibility to herbicides registered for use on established alfalfa.

S E N C O R / K A R M E X /V E L PA R L E X O N E G R A M OX O N E D I R E X T R E F L A N P OA S T K E R B E P TA M 2 , 4 - D B

WINTER ANNUAL WEEDS

Shepherdspurse C C P C N N N P P–C

Flixweed/Tansymustard C C P–C C N N N N C

Jim Hill mustard C C P C N N N N C

Field pepperweed C C C C N N N — C

Yellowflower pepperweed P–C C C C N N N — C

Downy brome (cheatgrass) C C C P C P–C C C N

Hare barley (foxtail) C C C C C C C P N

Wild oats P–C N P N–P N C C C N

Volunteer cereals P–C P C C N C C C N

S E N C O R / K A R M E X /V E L PA R L E X O N E G R A M OX O N E 1 D I R E X T R E F L A N P OA S T K E R B E P TA M 2 , 4 - D B

SUMMER ANNUAL WEEDS

Pigweed C C N–P C P N N C C

Lambsquarters P P N–P C P N N C C

Russian thistle P P — P P N N P P

Common sunflower — — — — — — — — C

Dodder N N N–P N C N P N N

Prickly lettuce C C P–C P–C N N N P C

Witchgrass P P — P C C C C N

Green foxtail (bristlegrass) N P N P C C P C N

Lovegrass (stinkgrass) P — — C C C C C N

Barnyardgrass P C P P C C N C N

S E N C O R / K A R M E X /V E L PA R L E X O N E G R A M OX O N E D I R E X T R E F L A N P OA S T K E R B E P TA M 2 , 4 - D B

PERENNIAL WEEDS

Swamp knotweed — — N–P — N N N — P

Chicory — — — — — — — — P

Common dandelion N–P P — — N N — — C*

Cheeseweed P* P* P P N N N N N

Canada thistle N N P* — N N N N P*

Bull thistle — — P* — N N N N C*

Povertyweed — — — — — — — — —

Buckhorn plantain N–P — — N–P N N N — C*

Bulbous bluegrass P–C C C P P — C — N

Foxtail barley P C* P–C P–C* — — C P–C N

Squirreltail — — — — — — C — N

Kentucky bluegrass P P P — N P C — N

Quackgrass P* — N P N P C P N

Perennial ryegrass — — — — — — C — N

Tall fescue — — — — — — C — N

Muhly — — — — — — C — N

Meadow foxtail — — — — — — C — N

C = control; P = partial control; N = no control; * = control of seedling weeds only; — = no information available.1. Gramoxone is not usually applied when summer weeds have emerged.

but weeds up to 6 inches tall can be treated.Gramoxone is strictly a postemergence contact herbi-cide; once it comes into contact with soil, or with evena thick layer of dust on leaves, it is deactivated. Forbest results, apply it after most of the weeds haveemerged (in March in most areas). However, neverapply it after alfalfa has 2 inches of growth. LassenCounty studies showed that treating alfalfa when itwas 4 inches tall rather than 1 to 2 inches tall resultedin a 0.5-ton yield reduction.

Always add a nonionic surfactant with Gramoxone;otherwise, weed control will decrease significantly. Thevisible effects of Gramoxone are observable afterapproximately 4 days. An evaluation of control can bemade after 7 days. If the growing point is not visiblydesiccated, weeds may recover.

Gramoxone can be tank-mixed with low rates of asoil-active photosynthetic inhibitor. The addition ofthe photosynthetic inhibitor (Velpar, Karmex, orSencor) retards the initial contact activity ofGramoxone. Tank mixing improves the effectiveness ofGramoxone and broadens the spectrum of weeds con-trolled. The combination of Gramoxone and a photo-synthetic inhibitor is particularly well suited toapplication in March, when most weeds have emergedbut rainfall may be insufficient to incorporate soil-active herbicides. As with Gramoxone alone, treatmentmust be made before alfalfa has 2 inches of growth. Anapplication window of approximately 2 weeks usuallyoccurs in March, depending on the year and location.The tank mix is effective when applied to soils high inorganic matter where soil-active herbicides alone havesometimes failed.

Application timing for winter-weed controlProper application timing is essential for effective weedcontrol and for avoidance of crop injury (Table 6.6).Soil-active herbicides can be applied anytime betweenNovember and February, when alfalfa is dormant.However, treatments from late December to earlyJanuary may be difficult because soil-active herbicidesshould not be applied to frozen or snow-coveredground. Although not common, applications inNovember to early December have several advantages.Because alfalfa is completely dormant, risk of injury iscomparatively low. The likelihood of sufficient precipi-tation for incorporation of herbicides is greater and thecost is usually less (soil-active herbicides do not need

to be combined with Gramoxone). Weed control isoften better because many of the winter annual weedshave not emerged or are very small. Disadvantages arethat some weeds may escape treatment when rodentactivity brings untreated soil to the surface. Also, areastreated with a soil-active herbicide cannot be reseeded,which may be necessary when winterkill of alfalfa issevere.

Provided soils have thawed and snow has melted,soil-active herbicides can also be applied in lateJanuary through February and as late as March inhigh-elevation valleys. This may be difficult when win-ters are severe. As soon as snow melts or soils thaw,alfalfa resumes growth. If herbicides are applied afteralfalfa has broken dormancy, yellowing (chlorosis) ofalfalfa and reduced yields occur (color photo 6.4).Symptoms of late treatment may not be apparentunless treated areas can be compared to untreatedareas.

Apply Gramoxone, or tank mixes of Gramoxoneand soil-active herbicides, in spring, before alfalfa hasgrown 2 inches. If growth is greater than 2 inches, donot use an herbicide; consider early mowing if weedinfestation is severe.

S U M M E R A N N U A L W E E D C O N T RO L

A dense, vigorous alfalfa stand permits little light toreach below the canopy, preventing summer annualweeds from becoming established. Proper fertilization,irrigation, and production practices usually make anherbicide application unnecessary. Residual activity ofwinter herbicides in soil also helps lessen, but does notalways eliminate, summer annual weed problems. Forexample, soil residual from Karmex controls lamb-squarters but is only partially effective for green foxtail(bristlegrass) control.

Occasionally, pigweed, lambsquarters, green foxtail,Russian thistle, and other weeds infest second andthird cuttings. These weeds, with the possible excep-tion of green foxtail, are usually a problem only inolder, depleted stands. Green foxtail is an aggressivesummer annual grass (Figure 6.2). It has been a majorproblem in the Central Valley of California for manyyears and is an increasing problem in some areas of theIntermountain Region. Trifluralin (Treflan TR–10) is

w e e d s 61

very effective against green foxtail, barnyardgrass, andmost common summer annual broadleaf weeds. ApplyTreflan in March to early May, before summer annualweed emergence (actual date depends on area).Rainfall or overhead irrigation must follow within 3days, or else reduced weed control may result. Becauseof the short growing season and small number of cut-tings in the Intermountain Region, reducing the ratesor using Treflan every other year is usually sufficientfor excellent summer annual weed control.

Poast (discussed earlier, in the seedling section) canalso be used to control green foxtail. After first or sec-ond cutting, apply Poast to emerged green foxtail priorto seedhead formation. Green foxtail should not bemoisture-stressed at the time of application. Delayapplication until after an irrigation if grasses are mois-ture-stressed, but do not apply Poast if alfalfa growthprevents spray coverage of the grass.

P E R E N N I A L W E E D C O N T RO L

Several perennial weeds—such as dandelion, quack-grass, bluegrass (both Kentucky and bulbous), andbuckhorn plantain—commonly infest intermountainalfalfa fields. Perennial weed invasion is favored by the

lack of tillage during the life of an alfalfa stand.Perennial weeds can be extremely difficult to control inestablished alfalfa. This is especially true for perennialbroadleaf weeds; to selectively remove a perennialbroadleaf weed from a perennial broadleaf crop such asalfalfa is almost impossible.


Figure 6.2. Green foxtail (commonly called bristlegrass) is anincreasing problem in portions of the intermountain alfalfa production region.

Table 6.6. Application times for herbicides registered for use in established alfalfa fields.1

TIME WINTER ANNUALS SUMMER ANNUALS PERENNIAL WEEDS

Nov.–Feb. Velpar (with surfactant) Kerb

(before fields turn green) Lexone/Sencor

Karmex/Direx

Feb.–Mar. Velpar (without surfactant)

(some weed growth before alfalfa Lexone/Sencor

shows any green) Karmex/Direx

Karmex/Direx plus Velpar Karmex/Direx plus Velpar

Mar. Gramoxone

(before alfalfa spring growth is Gramoxone plus Velpar

2 in. tall) Gramoxone plus Lexone/Sencor

Gramoxone plus Karmex/Direx

Mar.–early May Treflan TR-10

May–Aug. Poast Poast

1. Slash (/) between herbicides means that the names cited are 2 different trade names for the same chemical.

Proper site selection is a key component of perenni-al weed control. Avoid planting alfalfa in fields heavilyinfested with perennial weeds such as quackgrass, dan-delion, or Canada thistle. Prior to planting alfalfa,control these weeds through crop rotation, mechanicalcontrol, or with nonselective herbicides. An applica-tion of Roundup in the fall, prior to planting alfalfa, iseffective. Plowing or multiple discings prior to plant-ing can also control noncreeping perennial weeds,such as dandelion or buckhorn plantain. Also, avoidplanting in fields with poor drainage, because poordrainage will retard alfalfa growth but help many weedspecies to thrive.

After clean fields are attained, the best approach fordealing with perennial weeds is to prevent them fromreinvading. Sound cultural practices that maximize thecompetitive ability of alfalfa can minimize or delayencroachment by perennial weeds. A dense vigorousstand is by far the best defense against perennial weeds,because perennials first get a foothold in thin or weakareas of a field. Since most perennial weeds can be con-trolled in their seedling stage by using herbicides regis-tered for use in alfalfa fields, annual herbicide appli-cations prevent or delay perennial weed infestations.

Once perennial weeds become established in alfalfa,control options are limited. One option is to live withthe weeds. Fortunately, perennial weeds do not alwaysreduce the dietary value of the forage. For example,dandelions do not significantly detract from nutrition-al quality, though they do turn black after curing. Thisdetracts from the alfalfa’s appearance and reduces itsprice. When cut early, quackgrass-infested alfalfa isoften marketed to feed stores as alfalfa-grass mixed hay.However, most buyers of dairy-quality hay will notpurchase weed-infested alfalfa, so some method ofcontrolling established perennials in alfalfa is needed.

Soil-active herbicides suppress some perennialweeds (such as dandelion, quackgrass, and bluegrass)

after they become established. Velpar is usually themost effective. Kerb, applied at high rates (for exam-ple, 1.5 pounds active ingredient per acre), controlsquackgrass and Kentucky bluegrass. However, theserates are generally cost-prohibitive for alfalfa produc-tion. They are recommended only for spot treatmentof isolated grass patches or when pockets of perennialgrasses are observed in a relatively young field. Kerbapplications should be made before mid-February,when temperatures are cool and subsequent rainfall isordinarily sufficient to incorporate the chemical intothe soil.

Foliar-active herbicides have limited usefulness forcontrolling perennial weeds. Poast suppresses quack-grass, but repeated applications are needed to achievemeasurable control. This treatment is expensive for thedegree of control achieved. Therefore, treat quackgrasswith Poast only in the year of establishment, before therhizomes (underground stems) become too large anddifficult to kill. Roundup is effective for spot treat-ment of most perennial weeds but is not recommend-ed for widespread infestations; label restrictions permitno more than 10 percent of a field to be treated. Also,significant alfalfa injury can result if Roundup isapplied when alfalfa is not completely dormant (colorphoto 6.5).

T H E E C O N O M I C S O F C H E M I C A L W E E D C O N T RO L

Opting to treat alfalfa with herbicides can be a difficultmanagement decision. Several factors must be consid-ered: weeds species, their infestation level, alfalfa standdensity, herbicide cost, alfalfa market, and probabilityof successful weed control. For treatment to be economical, weed infestations must be severe enoughto reduce quality or alfalfa stand density. The value ofimproved forage quality or stand density must exceedthe cost of treatment. In addition, the alfalfa stand den-sity must be high enough to respond to the decreasedcompetition after weeds are controlled. Herbicideapplications to sparse, severely weed-infested standswill increase forage quality but can decrease total forageyield. Alfalfa does not spread into open areas, so remov-ing weeds in sparse stands often results in reinfestation.

The anticipated market for alfalfa hay sometimesdetermines if treatment is economical. For example,

w e e d s 63

A dense vigorous stand is by far the best defense

against perennial weeds

herbicides may be unnecessary when hay is fed to livestock (cattle or horses) on the ranch and weedinfestations are not too severe. Those who buy fordairies or feed stores, however, tolerate few weeds. If themarket demands high quality, herbicide treatment isusually justified. Herbicide treatment during standestablishment is often justified by an increase in alfalfastand density. Herbicides not only provide the immedi-ate benefit of weed control, but they also reduce weedseed reserves in the soil. Because of the depletion ofweed seeds in the soil, herbicide application every otheryear may be sufficient in some intermountain alfalfafields. This is often the case when seedling alfalfa fieldsare treated during the establishment year. A benefit ofweed control that is difficult to measure is the reduc-tion in weeds that occurs in subsequent crops.


Kempen, H. M. 1993. Alfalfa, forage. In Growers weed manage-ment guide, 3-18. Fresno, CA: Thompson Publications.

Mitich, L. W. 1985. Agronomic crops. In E. A. Kertz and F. O.Colbert (eds.), Principles of weed control in California, 231–75.Fresno, CA: Thompson Publications.

Mitich, L. W., H. Agamalian, C. Bell, M. Canevari, B. Fischer, G.Kyser, W. T. Lanini, V. Marble, R. Norris, S. Orloff, J. Orr, J.Schmierer, and R. Vargas. 1990. Weed control in seedling andestablished alfalfa in California. Oakland: University ofCalifornia Division of Agriculture and Natural Resources,Leaflet 21431.


Whitson, T. D., L. C. Burrill, S. A. Dewey, D. W. Cudney, B. E.Nelson, R. D. Lee, and R. Parker. 1992. Weeds of the west.Newark, CA: Western Society of Weed Science in cooperationwith the Western United States Land Grant UniversitiesCooperative Extension Services.


65

C H A P T E R S E V E N

I N S E C T SSteve B. Orloff and Roger W. Benton

�ne of the advantages of the intermountainenvironment as compared with other alfalfaproduction areas is that insect pests are rarely

a problem. Harsh winters and cool nights slow thedevelopment of insect pests. Therefore, in most years,insect populations do not reach levels that necessitatetreatment. On the rare occasions when insect pests arepresent in significant numbers, their damage can bedevastating to yield and quality. In fact, damagecaused by insect feeding often surpasses yield lossesdue to poor variety selection, low fertility, and mis-management. An effective pest management programcan preclude significant yield losses.

A pest management program should include thefollowing:

• correct identification of both harmful andbeneficial insects

• proper monitoring or surveillance of fields• reliable treatment thresholds• effective prevention and control methods

I N S E C T I D E N T I F I C AT I O N

The importance of proper insect identification cannotbe overstated. You must be able to distinguishbeneficial, innocuous, and harmful insects before youcan choose methods to encourage beneficial ones andprevent damage from harmful species. Insecticide treat-ments can sometimes be avoided when sufficient popu-

lations of beneficial insects are present (Figure 7.1).Effective prevention and control strategies have beendeveloped for most insect pests of alfalfa. The preferredpest management method varies depending on thepest, its population density, and environmental condi-tions. Pest management methods include plantingresistant varieties, harvesting at a time that lessens pestdamage, and using biological controls and insecticides.

Harmful insect populations must be kept belowthreshold levels. The threshold is that point at whicheconomic damage by an insect population is immi-nent and treatment is recommended. The Universityof California (UC) has developed treatment thresh-olds for most of the major insect pests. The thresholdsare linked to the value of the crop and can be adjustedin accordance with the anticipated market price. Theability to apply threshold data successfully depends onthe frequency of field monitoring, which in turndepends on the season and the pest. At the very least,you should sample fields once a week when pests arelikely to occur (Figure 7.2).

JAC

K C

LA

RK

The rest of this chapter describes the primary insectpests encountered in intermountain alfalfa fields. Foreach insect pest there is a description of its biology orlife cycle, the damage it causes, monitoring tech-niques, and recommended management programs forthe Intermountain Region. For more detailed descrip-tions and information (including color photographs)consult Integrated Pest Management for Alfalfa Hay,available from UC Cooperative Extension Offices.

A L FA L FAW E E V I L

Alfalfa weevil(Hypera postica) is the most destructive insect pest in

intermountain alfalfa fields. By chewing and skele-tonizing leaves, this pest can dramatically reduce yieldand quality. Larval feeding can be so severe that plantsare defoliated, giving the entire field a gray cast. Thealfalfa weevil is primarily a pest of the first cutting;when extreme population pressures occur, however,the effects of weevil feeding can carry over into thesecond cutting. Also, beware of alfalfa weevil damagein the second cutting if cool spring temperatures slowthe development of the insect.

Depending upon temperatures, weevil larvae mayappear in late March but are ordinarily most prevalentfrom mid-April to mid-June. A weevil larva is a smallworm about 3⁄8 inch long when fully grown. It is palegreen with a white stripe down the center of the bodyand a dark brown to black head (color photo 7.1).


Figure 7.1. Beneficial insects commonly found in alfalfa.

Damsel bug Minute pirate bug Big-eyed bug

Green lacewing(adult and larvae)

Ladybird beetle(adult and larvae)

Apanteles(alfalfa caterpillar parasite)

i n s e c t s 67

Alfalfa weevils have four instars, or growth stages.Initially, weevils are pale or yellowish. They become anincreasingly bright green as they develop. The first twoinstars feed on the tightly folded young leaves at theend of shoots, where they cause significant damage.These young worms can be difficult to locate, butsmall pinholes in young leaves signal their presence.The worms can be observed by carefully tearing apartthe terminal leaves of shoots, where weevil feeding isapparent. Compared to younger worms, third- andfourth-instar larvae are more voracious feeders andcause significantly more damage. Larvae completetheir growth in 3 to 4 weeks. Once mature, larvae spinsilken cocoons either on the leaves or, more common-ly, in debris on the soil surface (color photo 7.2). Theymature into adults 1 to 2 weeks later.

An adult weevil is dark gray to brown, with a darkbrown stripe on the back (color photo 7.3). It has adistinctive weevil snout approximately 3⁄16 inch inlength. Adults feed for a short time, not causingsignificant damage, before most leave the field andenter a resting stage. The resting period is usually

spent in weedy areas near the field or in field trash.Adults emerge in late winter or early spring, whenthey mate. Females deposit their eggs in alfalfa stems,completing the life cycle of the alfalfa weevil.

Management guidelinesAlfalfa weevil populations are monitored with a sweepnet. (Every grower should own a sweep net so thatinsects can be monitored on a regular basis. Contactyour local Farm Advisor’s office for a list of sweep netmanufacturers.) A standard insect sweep net is a 15-inch-diameter wire loop fitted with a cone-shaped netbag attached to a 26-inch handle. Once weevil larvaeare found, check the field every 2 to 4 days.

A single sweep consists of one 180-degree arc takenas you step forward (Figure 7.3). Hold the net verticallyso that the lower rim is 1 or 2 inches ahead of the upperrim and at least 4 inches into the alfalfa (Figure 7.4).This positioning will allow you to catch any insects thatfall from the plants. Take single or consecutive sweeps.In each field take several sweeps from all quadrants, andaverage the total number of larvae per sweep.

Parasitic wasps, Bathyplectes curculionis and others,have been released by U.S. Department of Agriculture(USDA) and Cooperative Extension researchers tokeep weevil populations low. Though these wasps maybe present, they often fail to keep weevil populationsbelow the threshold level. Unfortunately, there is littlea grower can do to initiate or encourage biologicalcontrol other than follow sound integrated pest man-agement (IPM) practices and use chemical treatmentsonly when necessary.

Weevils

Blue Alfalfa Aphid

Pea Aphid

Alfalfa Caterpillar

Armyworms

Cutworms

Clover root curculio

Blister beetles

Grasshoppers

Jan Feb Mar Apr May Jun Jul Aug Aug Oct Nov Dec

Figure 7.2. Seasonal occurrence of insect pests in the Intermountain Region.

Alfalfa weevil is the mostdestructive insect pest in

intermountain alfalfa fields.

At what point should you apply an insecticide?Implement chemical controls when counts approach20 larvae per sweep. Sometimes significant populationsof weevil larvae are present early in the season, beforethe alfalfa is tall enough to be swept. Under such con-ditions, use insecticides when 30 percent of the plantterminals show obvious signs of weevil feeding.

An alternative to insecticide treatment is early cut-ting of fields that are close to harvest. Weevil larvae areusually killed during harvesting. Occasionally, whenweevil populations are extremely high, enough weevilssurvive in the windrow to prevent alfalfa from regrow-ing. Therefore, carefully check regrowth for signs ofdamage to the second cutting.

A P H I D S

Both the pea aphid(Acyrthosiphon pisum)and the blue alfalfaaphid (Acyrthosiphonkondoi ) damage alfal-fa. They may be pre-sent in the field at thesame time as the alfalfa weevil but are usually foundslightly later (Figure 7.2). The pea aphid can survivewarmer temperatures than can the blue alfalfa aphidand can therefore be found later in the spring and mayeven occur in late summer or early fall. These twoaphids reproduce asexually and can multiply rapidly.Both are green, and they are similar in appearance.The easiest way to distinguish the two is to examinetheir antennae with a hand lens. Pea aphid antennaeare green with a narrow dark band at the tip of eachsegment; those of the blue alfalfa aphid are uniformlybrown (see color photo 7.4). Also, the blue alfalfaaphid is generally found on young tender shoots anddeveloping leaves, whereas the pea aphid can be foundover most of the plant. Ability to distinguish betweenthese two species is important because the blue alfalfaaphid is more damaging.

Both aphids can stunt alfalfa and reduce yield bysucking plant juices with their piercing mouthparts.They secrete a sticky substance referred to as honey-


Figure 7.3. A single sweep is one 180-degree arc taken as you stepforward. A sweep can be made singly or consecutively. To calculatethe average number of insects per sweep, simply divide the totalnumber of insects caught by the number of 180-degree sweeps.

Figure 7.4. Sweeping alfalfa for alfalfa weevil larvae. Hold the netvertically so that the lower rim is 1–2 inches ahead of the upper rimand at least 4 inches into the alfalfa.

dew. Honeydew can hinder the baling process, and itpromotes the growth of a black fungus that can reducethe palatability of the hay. In addition, the blue alfalfaaphid injects a growth-reducing toxin into the plant.

Management guidelinesFortunately, aphid populations in the IntermountainRegion seldom necessitate treatment. Predators, para-sites, and fungi keep aphid populations in check mostyears, but population explosions can occur. Considerbeneficial insect populations before applying an insecticide treatment. Common predators includeconvergent lady beetles (ladybugs), green lacewings,bigeyed bugs, minute pirate bugs, and damsel bugs(Figure 7.1). Aphid populations may increase wheninsecticides applied for control of the alfalfa weevil killbeneficial insects.

Resistant varieties of alfalfa have successfully mini-mized aphid damage. Alfalfa varieties resistant to peaaphid are readily available in the IntermountainRegion. Nondormant varieties resistant to blue alfalfaaphid are available, but resistance has not been incor-porated into most dormant varieties.

Stem samples are used to signal the need for aphidcontrol. Cut the stem close to the ground, and hit itsharply against a stiff piece of white paper or into awhite pan. This dislodges the aphids so they can becounted. Take several stems from different areas of thefield. Short alfalfa is more severely damaged than tallalfalfa; therefore, the treatment threshold variesaccording to the height of the alfalfa (Table 7.1).Treatment thresholds are high; the mere presence ofaphids in a field does not necessitate treatment. Asmentioned, aphid populations rarely reach these levelsin the Intermountain Region.

Sweep nets are used in some states to sample aphidpopulations. Although commonly used, this methodis not precise or efficient. Collection of 100 pea aphids

per sweep (a golf ball-sized ball of aphids) indicatesthe treatment threshold; for the blue alfalfa aphid, thetotal is lower.

C AT E R P I L L A R S

Alfalfa caterpillar (Colias eurytheme), beet armyworm(Spodoptera exigua), western yellowstriped armyworm(Spodoptera praefica), and alfalfa looper (Autographacalifornica) all feed on alfalfa during the summer.Temperatures are seldom warm enough for thesepests to be a serious problem in the IntermountainRegion, however.

Alfalfa caterpillarAlso referred to asalfalfa butterfly,this insect has avelvety green appearance. The larger larvae have awhite stripe down both sides of their body. An inva-sion of alfalfa caterpillars is preceded by a large influxof the adult form, a yellow or white butterfly. The lifecycle of the alfalfa caterpillar is closely synchronizedwith the cutting schedule of alfalfa. Infrequent cuttingand a short growing season usually prevent it fromreaching economically damaging levels in intermoun-tain alfalfa fields. Furthermore, a parasitic wasp(Apanteles medicaginis) is very effective in controllingthis pest; if alfalfa caterpillars are a suspected problemdetermine whether this wasp is present. Simply pullthe worm apart—if a white larva pops out, the alfalfacaterpillar has been parasitized.

ArmywormsBeet armyworm andwestern yellowstripedarmyworm are the mostcommonly occurring caterpillar pests. They appearduring the hot periods of July and August. A problemoften arises when one field is cut and armywormsmigrate to adjacent fields. Natural enemies can fre-quently control these caterpillars. Population levels arecyclic and armyworms only sporadically occur in largenumbers. In the Intermountain Region, the westernyellowstriped armyworm predominates.

Both beet armyworm and western yellowstripedarmyworm are smooth skinned. The beet armyworm is

i n s e c t s 69

Table 7.1. Treatment thresholds for pea aphid and blue alfalfaaphid.1

P L A N T P E A A P H I D / B LU E A L FA L FAH E I G H T S T E M A P H I D / S T E M

Under 10 in. 40–50

Over 10 in. 70–80 40–50

Over 20 in. 100

1. Data apply to the stem-shaking method of sampling, not to sweeping.This chapter describes the shaking method in the section on aphids.

most often olive green, but it ranges in color frombright green to purplish green. The western yellow-striped armyworm is usually black with orange stripesdown the sides. Both armyworms lay their eggs in clus-ters on the upper side of leaves. The eggs are coveredwith scales: Those of the beet armyworm are white andcottony, those of the western yellowstriped armywormgray. Larvae hatch and skeletonize leaves, causing alfalfaterminals to flag. These leaves make detection of army-worms relatively easy even from considerable distances.

Management guidelinesTable 7.2 lists treatment thresholds for summerworms. These thresholds are based on sweep netcounts using the same technique described in the alfal-fa weevil section. Both alfalfa caterpillars and army-worms are often controlled by parasites and diseases,so the presence of parasitized and diseased wormsshould be determined before treatment.

C U T W O R M S

Although a number of cut-worm species attack alfalfa inthe Intermountain Region, thevariegated cutworm (Peridromasaucia) is most common.Cutworms are occasional pestsin seedling alfalfa and less frequently a problem inestablished alfalfa. They can cause serious damage toseedling alfalfa fields by cutting off the seedlings at orjust below the soil surface. Cutworms injure estab-lished fields by cutting off new growth or feeding onalfalfa foliage.

Cutworms can be extremely frustrating to the grow-er because they are difficult to detect. They feed pri-marily at night and hide under debris or in cracks inthe soil during the day. Cutworms develop in weedyareas, later moving into an alfalfa field. Fully grownlarvae are smooth skinned, are 11⁄2 to 2 inches long,

and are brown, gray, or blackish. They often havestripes or spots on their back. When disturbed, cut-worms curl up. Adults are dull brown and gray mothsthat are nocturnal and often attracted to lights.

Management guidelinesCutworms are most injurious in fields with high plantresidue. Historically, cutworms are a problem in early,spring-seeded seedling fields. Tillage prior to seeding isan effective means of preventing cutworm damage.After seedling alfalfa has reached a height of at least 3inches, flood irrigation can significantly suppress cut-worm populations. A thorough harrowing may pro-vide adequate control when cutworms are activelyfeeding in established fields. Definitive monitoringand treatment guidelines have not been developedbecause cutworms are a sporadic problem. However,when the number of cutworms exceeds one or two perfoot of row or damage is severe, treatment is usuallywarranted. Spray in the late evening or night, whencutworms are actively feeding.

C L O V E R RO OT C U RC U L I O

The clover root curculio(Sitona hispidulus) adult is similar in appearance to thealfalfa weevil adult but is about one-third smaller andhas a shorter, blunter snout. It has a mottled brownishcoloration on its back rather than the dark brown“stripe” of the adult alfalfa weevil. The adult cloverroot curculio feeds on alfalfa foliage during the sum-mer and causes irregularly shaped notches in leaf mar-gins. The white grublike larval form causes the mostdamage by feeding on the roots. Larvae begin feedingon root nodules and fibrous roots and subsequentlychew large cavities along the sides of the taproot (colorphoto 7.5).

The clover root curculio overwinters as an adultunder trash and debris on the soil surface. Females lay


Table 7.2. Control action thresholds for summer worms.1

PEST NUMBER OF WORMS/SWEEP

Alfalfa caterpillar 10 nonparasitized and disease-free worms

Beet armyworm 15 nonparasitized worms 1⁄2 in. or longer

Western yellowstriped armyworm 15 nonparasitized worms 1⁄2 in. or longer

1. Data apply to the sweeping method of sampling, which this chapter describes in the section on alfalfa weevils.

their eggs on leaves or on the ground early in thespring. The larval stage lasts about 3 weeks. A larva isabout 1⁄4 inch long with a white body and a lightchocolate-colored head.

Management guidelinesClover root curculio has been found in numerousfields in the Intermountain Region. It is a perplexingproblem for several reasons. First, to detect a problem,the grower must dig up plants and inspect the roots.Second, the magnitude of damage caused by this pestis not well understood. Some suggest that larval feed-ing contributes to winter heaving and may enhancethe entry of disease organisms such as bacterial wiltand root rots. Some research has attributed significantlosses of quality, stand, and yield to the clover root cur-culio, but only when infestation is severe. Third, con-trol is extremely problematic; no insecticides areregistered for the control of clover root curculio andno resistant varieties of alfalfa have been developed.Plant stress from the feeding of clover root curculiolarvae is affected by soil moisture content, with greaterinjury occurring in dry soils. Therefore, maintainingsoil moisture at optimum levels is one method of miti-gating the effects of clover root curculio.

B L I S T E R B E E T L E S

Blister beetles are an occasion-al, isolated problem in parts ofthe Intermountain Region.Some species produce thetoxin cantharidin, an irritantthat can cause blisters on internal and external bodytissues. The toxin, not beetle feeding, is extremelysignificant because it causes sickness in livestock andcan even kill them. Even if beetles are killed, the prob-

lem may not be solved. Cantharidin remains in thebodies of dead beetles and can still cause injury if baledwith the hay. There are very few reported fatalities incattle and sheep, but contaminated hay can be deadlyto horses (cantharidin from only a few dead beetles can kill a horse). Therefore, do not sell blister beetle-infested hay to horse owners.

Blister beetles are rather large (1⁄2 to 1 inch long) andcan be various colors (black, gray, brown, or striped).They have long, soft cylindrical bodies and a pro-nounced “neck” area that makes them easy to distin-guish from other beetles. Blister beetles overwinter aslarvae in the soil and emerge as adults in the spring.Females deposit from 50 to several hundred eggs in soilcrevices. After hatching, larvae feed on grasshopper andcricket eggs. Adults fly into alfalfa fields, where theyfeed on alfalfa foliage. The beetles are usually found inlate spring and summer. Blister beetles are often worsein alfalfa fields adjacent to weedy grassy areas that con-tain an abundance of grasshopper eggs.

Management guidelinesBefore treating an alfalfa field, ascertain whether thebeetles contain cantharidin by having the beetles iden-tified by a trained entomologist. Treating blister beetlespecies that do not is probably unnecessary. Managingblister beetles is difficult. Treatment thresholds havenot been established, and chemical controls often donot eliminate the problem (because dead beetles canbe picked up in the hay and more beetles can migrateinto the alfalfa field). Several insecticides are registeredfor blister beetle control. Strip-spraying field edgesmay be the best approach when blister beetles areobserved in adjacent areas.

G R A S S H O P P E R S

Grasshoppers(Melanoplus spp.)are an infrequentproblem in alfalfa.However, left uncontrolled, severe outbreaks are capa-ble of destroying crops. Populations are often worst indrought years. Grasshoppers are most often a problemin isolated fields in foothill areas near weedy or grassyareas where they overwinter. Grasshoppers deposittheir eggs in soil in the fall and hatch in the spring. A

i n s e c t s 71

At the very least, sample fields once

a week when pests are likely to occur.

nymph, the immature form, becomes an adult in 40 to60 days. Mass migration of grasshoppers to alfalfafields from overwintering sites can occur in the spring,when the natural vegetation starts to dry.

Management guidelinesIn areas with a history of grasshopper infestations,check overwintering sites to detect potential problemswhile infestations are isolated and insignificant. Aneffective control measure involves creating a 60-footvegetation-free buffer strip around the field and apply-ing an insecticide bait to the strip. Insecticide use in afield is advised when grasshopper populations reach 20per square yard in field margins or 8 per square yardwithin the field. Spot treatment can be very effectivewhen grasshopper populations are isolated.

T H R I P S

Thrips (Frankliniellaspp.) are tiny insects withrasping mouthparts.These insects are verycommon in theIntermountain Region, and their feeding causes wrin-kled and distorted leaves (color photo 7.6). There areno data to suggest that they cause economic injury.Although leaves can be severely distorted and lookunsightly, treatment is not recommended.


Pedigo, Larry P. 1989. Entomology and pest management. NewYork: Macmillan.

Summers, C. G., K. S. Hagen, and V. M. Stern. 1993. Insects andmites. In B. Ohlendorf and M. L. Flint (eds.), Alfalfa pest man-agement guidelines, 1–19. Oakland: University of CaliforniaIPM Pest Management Data Base.

Summers, C. G., W. Barnett, V. E. Burton, A. P. Gutierrez, and V.M. Stern. 1981. Insects and other arthropods. In M. J. Haleyand L. Baker (eds.), Integrated pest management for alfalfa hay,42–63. Berkeley: University of California Division ofAgricultural Sciences, Publication 4104.


73

C H A P T E R E I G H T

N E M ATO D E SHarry L. Carlson and Becky B. Westerdahl

�lant-parasitic nematodes are microscopic,nonsegmented roundworms that feed onplants and may cause yield or stand loss

(Figure 8.1). Over 10 different types of plant-parasiticnematodes have been found in California alfalfa fields,but only two types—stem nematode (also called stemand bulb nematode) and root-knot nematode—havebeen associated with serious alfalfa crop damage innortheastern California. A third type, root-lesionnematode, is common in the region and has beenshown to injure alfalfa in other areas. However, seriousproblems with root-lesion nematode in alfalfa innortheastern California have been rare.

S T E M N E M ATO D E

Significant alfalfa yield losses may occur in fields in-fested with stem nematode (Ditylenchus dipsaci). Thisnematode infests alfalfa stems and crowns. Affectedstems are stunted and often turn yellow. Young infest-ed shoots appear swollen, with shortened internodes,which gives the stems a dwarfed appearance (colorphoto 8.1). The thickened stems are usually spongyand brittle and are especially prone to frost damage—they may succumb to only moderate frosts. The stemnematode also attacks buds and leaves and maydestroy young seedlings if present in large numbers.

Normally, symptoms of stem-nematode damageappear in patches of the field, reflecting the patchy distribution of the nematode (color photo 8.3). Thenematode moves in free water, so infestation and

damage are most severe during moist, cool, cloudyperiods, when water films persist for extended times.Accordingly, stem nematode is most often a problemin cool inland valleys under sprinkler irrigation or infoggy coastal areas. In the Intermountain Region,stem nematode may present a problem only in the firstor possibly the second cuttings, because hot, dry sum-mer weather reduces nematode activity. Crop damageand yield loss from this nematode can be severenonetheless.

Nematode infestation begins in one or more stemsand, if weather conditions remain favorable, spreadsthroughout the crown. The nematode persists in thealfalfa crown throughout the year. When alfalfa is not

Head of pin: 1.4 mm

Stem nematode: 1.3 mm

Figure 8.1. Plant-parasitic nematodes are too small to identify withthe naked eye. Note the size of a stem nematode in relation to thehead of a pin.

being grown, the nematode survives in plant debris oron the soil surface. Stem and bulb nematodes arespread from field to field in infested plant debris thatmay be carried by harvest or tillage equipment, wind,irrigation water, or animals.

RO OT- K N OT N E M ATO D E

Root-knot nematode infests and feeds on plant roots.It gets its name from the small galls that form on plantroots in response to nematode infestation. These gallscan generally be found in the branches of lateral rootsand distinguished from the nodules of nitrogen-fixingbacteria by gently rubbing the roots with your fingers(color photo 8.4). Nitrogen-fixing nodules are easilydislodged by rubbing; nematode root galls are not. Inaddition to root galls, root-knot nematodes often causean increase in the branching of lateral alfalfa roots.

Aboveground symptoms of root-knot nematodeinfestation are generally more difficult to identify than

are underground symptoms. With modest infesta-tion, symptoms may include noticeable yield loss orincreased plant sensitivity to nutrient or water stress. A severe nematode infestation may cause stunting inpatches of the field and result in yield loss.

Two species of root-knot nematode are of primaryconcern to alfalfa producers in the IntermountainRegion: the northern root-knot nematode (Meloido-gyne hapla) and the Columbia root-knot nematode(Meloidogyne chitwoodi). Two separate races ofColumbia root-knot nematode are present in theregion. Columbia root-knot nematode race 1 does notdo well or reproduce in significant numbers on alfalfa.

Columbia root-knot nematode race 2 attacks alfalfaroots and successfully reproduces on alfalfa host plants.

Often the most serious consequences of root-knotnematode infestations in alfalfa is the damage thenematodes cause in subsequent crops (Table 8.1).Following several years of alfalfa production, popula-tions of root-knot nematodes may be large enough toseriously injure higher-value crops such as potatoes,onions, or sugarbeets.

RO OT- L E S I O N N E M ATO D E

Female root-lesion nematodes (Pratylenchus spp.) laytheir eggs in root tissue or in the soil. Both larval andadult forms enter plant roots and migrate through roottissue while feeding on cell contents. Root-lesionnematodes are commonly found throughout theIntermountain Region. The two species most likely tobe found in the area are P. penetrans and P. neglectus.Of the two, P. penetrans is the more likely to injurealfalfa. Both species are capable of feeding on manycrop plants and weeds, but the extent to which theydamage crops, including alfalfa, is not clear. Reportedproblems caused by root-lesion nematode in alfalfa inthe Intermountain Region are rare. However, researchconducted in other regions of the United States hasshown that high root-lesion nematode levels can causeyield losses in established alfalfa and stand losses infields of spring-seeded alfalfa seedlings. Root-lesionnematodes have also been shown to predispose alfalfato infection by fusarium root and crown rot organisms.

Alfalfa may support fairly high populations of thesenematodes without apparent loss of yield. However, ifpopulations become extreme and environmental con-ditions are right for nematode development, alfalfaplant growth may become visibly stunted. Such stunt-ing is the only obvious symptom of root-lesion nema-tode infestation.

N E M ATO D E D E T E C T I O N A N D I D E N T I F I C AT I O N

Unfortunately, plant-parasitic nematodes in alfalfausually go undetected until visible plant injury occurs.When nematode damage is suspected, a nematologistmust examine the soil or infected plants to determine


Only . . . stem nematode androot-knot nematode

have been associated with serious alfalfa crop damage in

northeastern California.

n e m a t o d e s 75

the species involved. Many factors—such as nutrientstress, moisture stress, or severe weather—may causesymptoms similar to those caused by nematodes.

Take soil, root, and plant-tissue samples to a diag-nostic laboratory whenever alfalfa vigor seems limitedwithout an apparent cause. To begin this sampling,visually divide the field into areas that represent differ-ences in soil texture, drainage patterns, or croppinghistory. When soil is moist, take several samples fromeach area and include feeder roots if possible. Becausenematodes feed on roots, they are more prevalent inthe rooting zone of the current or previous crop thanelsewhere. A series of samples from throughout thefield is necessary because nematodes are usually notuniformly distributed. In an established field, collectsamples from areas that show symptoms and fromadjacent healthy areas. Sampling at the edge is usuallybetter than sampling the middle of an unhealthyarea—roots in the center of an infested area may betoo decayed to support a nematode population. Mixsamples from the same area together, and place 1quart of the mixed soil and roots into a plastic bag.

Seal the bag, place a label on the outside, keep thesamples cool (do not freeze them), and, as soon as pos-sible, take the bag to a diagnostic laboratory.Prolonged exposure of sealed plastic bags to directsunlight may cause sufficient heating to kill nema-todes. Be certain to inform the laboratory that alfalfais the current or planned crop for the field so the tech-nicians will use appropriate extraction techniques.Your local Farm Advisor can help you locate a diag-nostic laboratory.

Careful soil sampling and examination by aqualified nematologist can detect nematode problemsbefore planting. Because of the time and expenseinvolved, most growers do not test for nematodesprior to alfalfa planting, though such tests are donebefore planting higher-value rotation crops (such asonions or potatoes). Take the presence of nematodesin soil samples or previous crops into account beforeestablishing an alfalfa crop.

C O N T RO L

The primary tools available for nematode control inalfalfa are nematicides, resistant varieties, and croprotation. Cost precludes the use of nematicides in alfal-fa fields. However, nematicides may be economical forhigher-value crops grown in rotation with alfalfa.

Crop Rotation

Neither root-knot nematode nor stem nematode canpersist in the soil for long periods without a host crop.

When nematode damage is suspected, a nematologistmust examine the soil or

infected plants to determinethe species involved.

Table 8.1. Host potential of various crops in regard to root-knot nematode.

C RO P

N E M ATO D E

S P E C I E S A L FA L FA S M A L L G R A I N S P OTATO E S S U G A R B E E T S O N I O N S PA S T U R E G R A S S E S

Northern root-knot

M. hapla Host Nonhost Host Host Nonhost Nonhost

Columbia root-knot

M. chitwoodi race 1 Nonhost Host Host Host Host Possible host

Columbia root-knot

M. chitwoodi race 2 Host Host Host Host Possible host Possible host

Therefore, rotation with nonhost crops can be an effec-tive means of reducing soil populations of these pests.

Many races of stem nematode can infest many plantspecies; however, the most likely alternative hosts forstem nematode in northeastern California are redclover, ladino clover, and sweet clover. Two years ofcrop rotation to nonhost crops—such as small grains,sugarbeets, or potatoes—should reduce soil popula-tions below levels that cause economic loss in alfalfa.For a nonhost crop rotation to be effective, take care tocontrol all volunteer alfalfa in the rotation crop.

Crop rotation can effectively control root-knotnematode also, but proper identification of the root-knot species is critical to the selection of the rotationcrop. Different root-knot species and races prefer dif-ferent hosts (Table 8.1). For example, rotation to acereal crop is an effective way to lower soil populationsof northern root-knot nematode, but cereal rotationwill tend to maintain populations of Columbia root-knot nematode. Likewise, alfalfa is an excellent rota-tion crop for row crops infested with Columbiaroot-knot nematode race 1 but is unsuitable for con-trolling Columbia root-knot nematode race 2.

If no suitable nonhost crop can be identified, a yearof noncrop, weed-free fallow can be effective in lower-ing soil populations of root-knot nematode. For maxi-mum effectiveness, cultivate the fallow field duringthe fallow season. This disturbs nematodes and plantdebris and helps control weeds and volunteer alfalfathat may be nematode hosts.

Crop rotation may affect root-lesion nematodepopulation numbers, but it will probably not controlthe pest because of the number of crop and weedspecies that are suitable hosts for it.

Variety Resistance

If a field has a history of stem nematode infestation,plant it with alfalfa after crop rotation has lowered soilnematode populations. Use only varieties withdemonstrated resistance to stem nematode. Manyresistant varieties adapted to the IntermountainRegion are available.

Although some varieties are resistant to root-knotnematode, the value of this resistance is not clear-cut.This is largely due to the time, effort, and difficulty ofscreening alfalfa cultivars against all the root-knotspecies and races known to infest alfalfa. Before pur-chasing a variety, discuss the potential effectiveness ofcultivar resistance to specific root-knot nematodespecies with the seed dealer or with a University ofCalifornia Farm Advisor.

Varieties with resistance to root-lesion nematodeare not available, although breeding programs toincrease cultivar resistance to nematodes are inprogress.


Ferris, H., P. B. Goodell, and M. V. McKenry. 1981. General rec-ommendations for nematode sampling. Berkeley: University ofCalifornia Division of Agricultural Sciences, Leaflet 21234.

Lownsbery, B. F., W. H. Hart, J. D. Radewald, and I. J.Thomason. 1981. Nematodes. In M. J. Haley and L. Baker(eds.), Integrated pest management for alfalfa hay, 78-80.Berkeley: University of California Division of AgriculturalSciences, Publication 4104.

McKenry, M. V., and P. A. Roberts. 1985. Phytonematology studyguide. Oakland: University of California Division ofAgricultural Sciences, Publication 4045.


C H A P T E R N I N E

D I S E A S E SR. Michael Davis, Steve B. Orloff, and Kristen D. Marshall

�lfalfa is susceptible to a wide rangeof bacterial, fungal, and viral dis-eases. These diseases can attack

foliage, crowns, or roots and may substantially reduceyield, stand life, and forage quality. Some diseases canbe difficult to control because, except for seed treat-ment, no fungicides are registered for use on alfalfa.Fortunately, alfalfa diseases are not as economicallydamaging in the Intermountain Region as in otherparts of the state; the cold winters, short growing sea-son, and relatively dry conditions that prevail overmost of the region are not conducive to them.

Planting varieties with genetic resistance to themost prevalent diseases is the primary method of dis-ease management in alfalfa. Most diseases can beeffectively managed using this approach. However, afield planted to a variety classified as resistant maycontain diseased plants. Alfalfa is genetically diverse(heterogeneous), and there will always be some plantssusceptible to disease even in a resistant population.For example, in a variety rated as having resistance to aparticular disease, only 31 to 50 percent of the plantsare resistant (Table 9.1). Resistance ratings representthe results of standardized tests performed on seedlingplants. Such tests do not take into account variousgrowth stages and environmental stresses that mayinfluence diseases in the field. Therefore, genetic resis-tance should not be the only method used to controldiseases in alfalfa. Crop management, such as irriga-tion and harvesting practices, plays an important rolein preventing or minimizing losses caused by disease.

This chapter outlines the most predominant orpotentially threatening diseases in the IntermountainRegion. They are grouped into four categories: damp-ing-off diseases, root and crown rots, foliar diseases,and wilt diseases.

D A M P I N G - O F F D I S E A S E S

Several soilborne fungi cause early wilting and deathof young seedlings pre- or postemergence, a scenariocommonly referred to as damping-off. The causes ofdamping-off are species of Pythium, Phytophthora,Rhizoctonia, and Fusarium. These fungi are most com-

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mon in wet soils where drainage is poor or duringperiods of heavy rain or overirrigation. Damping-offtypically occurs during cool, wet conditions in thespring, and less often in the fall. Control measuresinclude planting at a rate that will allow for thinningdue to seedling diseases and planting at a time of yearwhen growing conditions favor rapid seedling devel-opment. Fortunately, seedlings more than 1 to 2weeks old rarely become infected with these diseases.

Damping-Off Caused by Pythium

Pythium species are the most common cause of seedrotting and damping-off in seedlings. These fungican greatly reduce a stand of alfalfa, especially in wetareas. Pythium survives in the soil or on crop residue.Swimming spores, called zoospores, infect seed orseedlings during periods of free moisture in the soil.Alfalfa seedlings become resistant to Pythium damp-ing-off about 5 days after emergence, but infectionof feeder roots can occur at any stage. Low tempera-tures and high soil moisture are favorable for diseasedevelopment. The disease tends to be more severe inacidic soils.

Seeds infected by Pythium during germination turninto a soft brown mass, or the seedling root andcotyledon leaves become brown and soft soon afteremergence. Infection at later stages causes lesions on

the shoot and root. The lesions eventually collapse,causing damping-off or stunting and small dark greencotyledons. The root appears pinched off (color photo9.1). Infected seedlings may fall over and die within afew days. Under optimal growing conditions, aseedling with a diseased primary root may survive byproducing secondary roots above the lesions.

To compensate for seed loss due to Pythium fungi,seed at a higher-than-normal rate. Also, see the discus-sion of fungicides in the next section, aboutPhytophthora.

Damping-Off Caused by Phytophthora

Symptoms of damping-off caused by Phytophthorafungi on seedling alfalfa are similar to those caused byPythium fungi. The area below the cotyledons(hypocotyl) becomes water-soaked and limp, then collapses and withers. Seedlings are stunted and havesmall, dark green cotyledons and die within a few days.

A seed treatment fungicide, such as metalaxyl(Apron), can be used as a seed dressing to protectagainst seedling diseases caused by Pythium andPhytophthora species. However, use has not been foundto be beneficial in tests in California; seed treatmentfungicides are recommended only where seedlingdamping-off is known to be a problem. The preferredmethod for controlling this disease in the field is tooptimize seedling growth by preparing a firm seedbedand adjusting soil pH and fertility to levels optimumfor alfalfa growth. Avoid overirrigation. Also, plantwhen soil conditions favor rapid emergence and earlyseedling growth, such as in late summer (see chapter 2).

Damping-Off Caused by Rhizoctonia

Rhizoctonia fungi are another cause of seedling damp-ing-off. Symptoms of this seedling disease include red-dish brown, shrunken lower stems and roots. Thesefungi require a food base before infecting a plant; thus,excessive organic residue in the soil encourages them.Excessive soil moisture also favors them. However,unlike the seedling damping-off diseases already men-tioned, infection by Rhizoctonia generally occurs dur-ing periods of high temperature and can affectseedlings at any growth stage.


Table 9.1. Plant resistance ratings.

P E RC E N TA G E O F R E S I S TA N T P L A N T S R E S I S TA N C E C L A S S

0–5 Susceptible

6–14 Low resistance

15–30 Moderate resistance

31–50 Resistance

>50 High resistance

Phytophthora root rot is only important where soil-

water is excessive.

d i s e a s e s 79

No control measures are generally taken againstRhizoctonia. Ensuring decomposition of organic mat-ter by adequately incorporating plant residue prior toplanting alfalfa seed may reduce seedling infection.

RO OT A N D C ROW N ROT S

Root and crown rots are the most common and pos-sibly most devastating diseases of alfalfa. They can becaused by a complex of fungi, including Phytophthoraspp., Stagonospora meliloti, Rhizoctonia spp., andColletotrichum trifolii. Stand decline is the mostnoticeable symptom. Decline usually begins duringthe 2nd year after planting and gradually becomesmore severe. Early symptoms include yellowing andwilting of stem tips or entire shoots, which eventuallydie. Plants may be stunted and have an increasednumber of small, shortened stems and small leaves.Crowns of infected plants always exhibit some degreeof rot. Control is difficult. This disease complex is amajor factor contributing to early stand decline.

Phytophthora Root and Crown Rot

One of the primary organisms responsible for root andcrown rot is Phytophthora megasperma. It is soilborneand occurs wherever alfalfa is grown. The greatestdamage occurs under flood irrigation and with poorlyleveled and poorly drained soils. Phytophthora rootand crown rot can be injurious to seedling stands, butit is more commonly a problem in established fields.

Although Phytophthora fungi primarily infect roots,symptoms are expressed in all parts of the plant.Leaves wilt, turn yellow to reddish brown, and drop.Plants grow slowly after cutting and may wilt and die.Root symptoms are diagnostic for this disease. Tan tobrown lesions on taproots usually appear where a lat-eral root emerges. Lesions eventually turn black; thecenter of the root is yellow. Taproots can be affected at any depth where water drainage is impeded. Red-orange to yellow streaks spread up several inches fromthe rotted end of the root (color photo 9.2). This dis-ease can devastate large areas of a field, but frequentlyonly individual plants are affected.

Phytophthora root rot is only important where soil-water is excessive. The fungi can survive for long

periods in an inactive state in soil or in plant debrisand become active when there is too much water. Rotcaused by Phytophthora is most common at the tailend of flood-irrigated alfalfa fields. Spores of thesefungi can be carried in irrigation water. Thus, if tailwater is channeled from an infected field back to anirrigation canal, the disease can spread. The most fre-quent points of infection are the tips of small rootsand the bases of fine lateral roots. The disease may belimited to a portion of the root or may spread up thetaproot to the crown. If the crown becomes infected,the plant will likely die as soon as 1 week after infec-tion. If infection is limited, the plant may continuegrowing at a reduced rate, but it will be far more sus-ceptible to winter injury.

Soil and water management is the most importantcultural control. Reduce the amount of time that soilis saturated by reducing soil compaction with deeptillage (see chapter 2). Reducing the length of floodirrigation runs, shortening irrigation time, and level-ing land all help alleviate disease severity. Cultivarsresistant to phytophthora root rot are available; usethem along with sound cultural practices in fieldsknown to have problems with Phytophthora fungi.

Stagonospora Root and Crown Rot

Crown and root rot caused by the fungus Stagonosporameliloti is widespread in California but is not a majorproblem in the Intermountain Region. It can be one ofthe primary reasons for early stand decline, however.The vigor of an alfalfa stand decreases because of a slownecrosis, or dying, of crowns. Bark tissue on infected

Alfalfa is genetically diverseand there will always be some

plants susceptible to diseaseeven in a resistant population.

roots and crowns is often cracked. A diagnostic symp-tom is the presence of red flecks in root tissue. Fine redstreaks also occur in the xylem (the water-conductingtissue) in the center of the root, below rotted portionsof the crown. The pathogen may also infect leaves,causing irregular tan lesions and defoliation.

Spores of S. meliloti are spread by water that splash-es on infected leaves, stems, or plant debris. The fun-gus enters the crown through stems and grows slowlydownward into the taproot. Although the infectioncan take 6 months to 2 years to kill a plant, it reducesplant vigor and yield. Leaves and stems are generallyinfected during spring rains, but crown infections canoccur anytime. The disease is most damaging whenalfalfa is not actively growing.

No resistant cultivars are available. Rotation out ofalfalfa for 2 or 3 years eliminates sources of inoculumwithin a field.

Rhizoctonia Root and Crown Rot

This disease, caused by Rhizoctonia fungi, attacksestablished as well as seedling alfalfa. It occurs wherev-er alfalfa is grown and at any stage of plant growth.Root cankers are tan or buff elliptical, sunken lesions.When the pathogen is inactive during cool months,cankers heal and turn black. If the lesions girdle thetaproot, the plant may die; otherwise, new roots willemerge and the plant will survive.

Rhizoctonia species persist in soil as sclerotia (aninactive stage of fungal development) associated withplant residue. They can also survive saprophytically—that is, living on dead organic matter—in the absenceof a living host. These fungi require a food base beforeinfecting a plant; thus, excessive organic matter in thesoil favors the disease. After entering through wounds,the fungi travel from lateral roots to taproots and fromcrowns to crown buds. High temperatures and exces-sive soil moisture promote rhizoctonia rot.

No control measures are generally practiced. To reduce seedling infection, ensure decomposition of organic matter by adequately incorporating it beforeplanting.

Anthracnose

Anthracnose, caused by the fungus Colletotricum tri-folii, is a sporadic and relatively rare problem in theIntermountain Region, but, when it occurs, losses canbe significant. Anthracnose can affect leaves, stems,and crowns of alfalfa, but crown rot has been the mostsignificant symptom in the Intermountain Region.The most apparent symptom of anthracnose is thebluish black, V-shaped rot that can be observed on the crown when dead stems are removed. On stems,anthracnose causes small irregularly shaped blackenedareas that may become large, sunken oval or diamond-shaped straw-colored lesions with black borders (colorphoto 9.3). Black fruiting bodies, which under a handlens look like small dots, develop in the lesion. Aslesions enlarge, they may coalesce, girdle, and kill oneto several stems on a plant. In summer and fall, deadshoots (straw to pearly white in color) are scatteredthroughout the field.

The fungus persists in alfalfa debris and crowns.The disease reaches maximum severity during latesummer and early fall. During the growing season,spores on stem lesions are a source of inoculum.Spores may also be spread with seed contaminatedduring the threshing process.

Anthracnose spreads rapidly during warm andhumid weather. Splashing rain and irrigation waterdisperse spores onto growing stems and petioles.

To control anthracnose, grow resistant cultivars.Clean debris off all harvesting equipment before thefirst spring harvest and also during the growing seasonwhen moving from an infected to a noninfected field.Cut infected alfalfa before losses become too severe.Rotating with crops other than clover and alfalfa for 2years or more will eliminate sources of inoculum inthe field.

F O L I A R D I S E A S E S

Several foliar diseases attack alfalfa, including com-mon leaf spot, stemphylium leaf spot, spring blackstem, and downy mildew. Of these, downy mildew isgenerally the only foliar disease of concern in theIntermountain Region.


Downy Mildew

Downy mildew, caused by the fungus Pernospora trifo-liorum, occurs in cool, wet, or humid conditions and isfavored by sprinkler irrigation. It can be found any-time during the growing season in the IntermountainRegion but is most common in spring. Damage ismost serious in seedling alfalfa fields. Loss from downymildew in established stands is usually restricted to thefirst cutting.

Downy mildew is easy to distinguish from otherfoliar diseases; the symptoms it causes are unique.During cool moist weather or when humidity is high,a fine grayish growth of spores is usually apparent onthe underside of leaflets. The upper side of infectedleaves is light green to yellow (color photo 9.4).Symptoms are usually restricted to portions of leaflets,but, if the infection is systemic, they may appear onentire leaves or shoots. Infected leaves are twisted andcurled. On infected stems the internodes (the stemareas between leaves) are shorter and thicker thanthose of normal stems. Plant growth is stunted.

Pernospora trifoliorum overwinters as resting sporesin the crown of surviving plants and in plant debris.Spores are produced during periods of near-100-percent relative humidity. They are fragile and survivefor several hours to a few days, depending on environ-mental conditions. Dispersal is primarily by wind andsplashing rain. Spores fall on young, susceptible leavesand germinate in free water. Germination of sporesoccurs from 39º to 84ºF (4º to 29ºC), with optimumgermination at 65ºF (18ºC). The fungus produceslarge numbers of spores during periods of abundantmoisture.

Cultivars resistant to downy mildew have beendeveloped and are the most economical means of con-trol. However, varietal resistance is not well document-ed, so choosing a resistant cultivar is difficult.Fortunately, downy mildew is rarely of economicimportance in the Intermountain Region, and growerscan manage it with cultural practices. Allowing longerintervals between irrigations, with more water per irrigation, can help reduce symptoms if fields aresprinkler irrigated. In rare cases when mildew is severe,cut alfalfa early to save foliage. Harvesting removes theinoculum source of the short-lived spores, removesyoung susceptible leaves, and reduces the relativehumidity of the plant canopy. Normal increases in sea-

sonal temperatures reduce the chance of downymildew reinfection.

W I LT D I S E A S E S

Bacterial Wilt

Bacterial wilt, caused by the bacterium Clavibacterinsidiosum, is present wherever alfalfa is grown, but itis rarely seen today due to the development of wilt-resistant cultivars. Infected plants are easily detected bytheir yellow-green color and stunted growth. Diseasedplants may be scattered throughout the field. Mildlyaffected plants are short. They have mottled leaves andslightly cupped leaflets or leaflets that curl upward.Severely diseased plants are stunted, are yellow-greenin color, and have spindly stems and small, distortedleaflets (color photo 9.5). Disease symptoms are mostevident in regrowth after clipping. A cross section ofan infected taproot reveals a yellowish tan color in thecenter. Often, small areas or pockets on the inside ofthe bark tissue turn brown.

The bacterium survives in plant residue in soil andenters plants through wounds in the roots and crownor through the cut ends of freshly mowed stems. Oncea susceptible plant is infected, it usually does notrecover. Disease symptoms rarely appear before the2nd or 3rd year. Plants die within 5 to 8 months aftershowing symptoms. Disease severity and incidenceincrease with the presence of nematodes. The bacteri-um can survive in dry plant tissue or seed for at least10 years and can be disseminated over long distancesin seed and dry hay. However, populations of theorganism in the soil decline quickly when infectedplant residue decomposes. Bacterial wilt can be spreadby surface water, tillage, mowing, and harvestingequipment. Plants with bacterial wilt are prone to win-ter kill. The greatest incidence of the disease occurs inpoorly drained areas of fields; large areas can be infect-ed during periods of continuous wet weather.

Resistant cultivars keep the disease under control.Nearly all dormant alfalfa varieties currently marketedare rated as resistant or highly resistant to bacterialwilt. If you discover the disease in a susceptible culti-var, limit disease spread by mowing new stands beforeold stands. Also, do not mow wet plants.

d i s e a s e s 81

Fusarium Wilt

Fusarium oxysporum is a fungus that causes fusariumwilt, which occurs wherever alfalfa is grown. The dis-ease is not generally important in the IntermountainRegion because of the availability of resistant cultivars.Fusarium wilt progresses over several months. Thefungus enters roots through wounds in the taproot andcontinues into the xylem, or water-conducting tissue.Shoots and leaves may wilt during the day but regainturgidity at night. As the infection progresses, stemsbecome bleached. Toxins produced by the fungus dis-color host tissue; a red discoloration appears on leaves.The xylem eventually becomes plugged, causing death.Fusarium wilt can be identified by the dark reddishbrown discoloration in the stele, or center, of the tap-root (color photo 9.6). Fusarium oxysporum may per-sist in soil for several years.

Fusarium wilt is more severe when plants are infest-ed with root-knot nematodes. Soil moisture does notaffect the severity of the disease, but high soil tempera-tures favor infection.

Cultivars with resistance to both fusarium wilt androot-knot nematode offer the best control when bothorganisms are present. Sound cultural practices thatencourage alfalfa growth reduce incidence of the disease.

Verticillium Wilt

Verticillium albo-atrum, a fungus that causesVerticillium wilt, was first found in the United States

in 1976 on alfalfa growing in the Yakima Valley and inthe Columbia Basin of central Washington. Sincethen, it has been reported in most northern states,south to Kansas and Maryland. It has also been foundin the high desert of Southern California and thecoastal counties of central and northern California. Itwas discovered in the summer of 1993 in theIntermountain Region, but the extent of its spread isunknown at this time.

Verticillium wilt is a potentially serious problem; itcan reduce yield by up to 50 percent and shorten standlife severely. It has been an insidious problem over sea-sons and years rather than a devastation in a singleyear. Note that the disease is usually only expressedunder certain environmental conditions (cool wetweather followed by hot days). Therefore, the funguscould exist in a field that appears healthy. Also, the dis-ease is apparently more serious in irrigated fields thanin dryland fields.

Verticillium wilt symptoms are distinctive, but lab-oratory analysis must verify field diagnosis. Diseasedplants are usually scattered throughout the field. Atfirst glance, the symptoms look like gopher damage,except that the plants do not pull out of the ground.

A V-shaped yellowing, or chlorosis, discolors leaflettips (color photo 9.8). At the end of the stem, themargin of some leaflets is rolled (color photo 9.9).Leaves on individual stems dry, turn brown, and mayfall off. Infected stems do not wilt and often retaintheir green color until all the leaves are dead.Internodes (the stem areas between leaves) are oftenshort toward the end of a stem. Eventually, thepathogen spreads to the crown, and affects all thestems, and the plant wilts and dies. Although internalroot tissue can turn brown, this reaction is variableand is not a dependable symptom for diagnosis.

Contaminated hay and pellets can introduce thepathogen into new areas. The disease can also bespread by the manure of animals who ate infected hay,by insects, by water, and by infected seed. The windcan disseminate fungal spores (conidia) over short dis-tances. Verticillium albo-atrum does not usually survivemore than 1 year in field debris after an infested field istaken out of alfalfa production. It can survive up to 3years in dry hay. It can also survive in several weedspecies, including Medicago spp., but does not cause


Fusarium wilt is not generally important in the

Intermountain Region because of the availability

of resistant cultivars.

problems for most other crops. Verticillium dahliae, arelated fungus, causes wilt of many other plant speciesbut not alfalfa.

Verticillium albo-atrum grows best between 68 and77ºF (20º to 25ºC). The pathogen survives the tem-peratures used to produce dehydrated alfalfa productsand can pass unharmed through the digestive systemof sheep.

As a control for verticillium wilt, crop rotation haslimited effectiveness because the pathogen can surviveon several broad-leaved weeds. However, if crop rota-tion and weed control are practiced, the inoculum canbe significantly reduced in 2 to 3 years. Avoid intro-ducing the pathogen on contaminated hay. Cleanplant debris from equipment with high-pressure wateror steam before entering new fields. Cut clean fieldsbefore diseased fields.

Planting resistant varieties is by far the best methodto control the disease. Fortunately, most certified dor-mant varieties are relatively resistant. The University ofCalifornia recommends planting only resistant (R) or

highly resistant (HR) varieties in the IntermountainRegion (see chapter 3). Resistant varieties have keptverticillium wilt from becoming an economicallysignificant disease in areas of the Pacific Northwest,where the fungus has been present for many years.


Gilchrist, D. G., R. F. Brewer, D. C. Erwin, D. H. Hall, J. G.Hancock, A. Martense, and O. Ribiero. 1981. Alfalfa plantdiseases. In M. J. Haley and L. Baker (eds.), Integrated pestmanagement for alfalfa hay, 64–77. Berkeley: University ofCalifornia Division of Agricultural Sciences, Publication 4104.

Graham, J. H., F. I. Frosheiser, D. L. Stuteville, and D. C. Erwin.1979. A compendium of alfalfa diseases. St. Paul, MN: AmericanPhytopathological Society.

Peaden, R. N., and A. A. Christen. 1984. A guide for identificationof verticillium wilt in alfalfa. USDA Agriculture InformationBulletin No. 456.

d i s e a s e s 83

C H A P T E R T E N

V E RT E B R AT EP E S T SSteve B. Orloff, Terrell P. Salmon, and W. Paul Gorenzel

�ertebrate pests are often a serious problemin the Intermountain Region ofCalifornia. Rodents (gophers, ground

squirrels, and meadow mice) are the most injurious ofthe vertebrate pests. In annual cropping systems, fre-quent field cultivation usually discourages large rodentcolonies. In the intermountain area, however, theeffects of cultivation are offset by the predominance ofperennial crops adjacent to uncultivated land. Forrodents, alfalfa fields are highly desirable habitat.

Vertebrate feeding and nesting behavior cause arange of problems to above- and belowground por-tions of alfalfa plants. In addition, burrowing activity—particularly by pocket gophers and the Beldingground squirrel—can disrupt harvest operations anddamage harvest equipment. Mounds caused by bur-rowing can cover plants, resulting in further produc-tion losses. Burrowing also adversely affects theefficiency of irrigation systems, primarily in flood-irrigated fields.

Many pests are managed using the concept ofthreshold levels. In other words, when the pest popu-lation density reaches the level where control is econ-omically justified, control measures are undertaken.This approach is less useful for vertebrate pests thanfor others, because treatment threshold levels have notbeen developed. Very low vertebrate pest populationscan be tolerated. Their great reproductive capacity

mandates that populations be maintained at low levelsto prevent an unmanageable population outbreak.Table 10.1 summarizes the control methods this chap-ter will discuss.

P O C K E T G O P H E R S

Pocket gophers (Thomomys spp.) are the most com-mon and often the most destructive vertebrate pest ofalfalfa. Unfortunately, alfalfa is a preferred food ofgophers, and it provides ideal conditions for gopherpopulation buildup. Pocket gophers feed primarily onthe taproot and often kill plants. Their feeding canlead to significant yield reduction, and their burrowscause damage to harvest machinery. The damage doneby gophers to an alfalfa stand is permanent; even aftergophers have been controlled, the effect of previousgopher feeding continues to affect yields.

Pocket gophers are (6- to 8-inch-long) stout-bodied, short-legged rodents well adapted for burrow-ing (color photo 10.1). The name pocket gopher refersto the fur-lined external cheek pouches, or pockets,used to carry food and nesting materials. The pocketgopher can close its lips behind its four large incisor

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Table 10.1. Vertebrate pest control measures for alfalfa.1

C O N T RO L M E A S U R E RO D E N T I C I D E T I M I N G C O M M E N T S

P O C K E T G O P H E R S

Hand-baiting Strychnine-treated Late winter and Useful for small isolated infestations. Strychnine-grain and throughout growing treated grain is more effective than anticoagulant baits.anticoagulant baits season

Mechanical Strychnine- Late winter to early Effective for widespread infestations. Proper soil moisturebaiting treated grain spring, before alfalfa content is critical. Use mechanical burrow builder only in

breaks dormancy. May areas where gophers are present, not as a preventive measure.be done throughout the growing season after a cutting.

Trapping Late winter and through- Effective but very time-consuming. Set traps in pairs, facingout growing season opposite directions.

G RO U N D S QU I R R E L S

Deep tillage Fall or spring Deep tillage destroys burrow system and is (fall preferred) believed to reduce populations.

Shooting Whenever observed Time-consuming, expensive, and marginally effective for large infesta-above ground tions. Most effective when squirrels first emerge after hibernation.

Fumigation Acrolein When squirrels emerge Effective but time-consuming. Retreatment of(Magnacide) after hibernation (Feb.) survivors improves control considerably. Concentrate

through June efforts on low infestations or young fields.

Gas cartridges March through June Usually only 30 to 40 percent effective, possibly due to cold, dry soils. in the spring. Follow-up treatments improve control.

Aluminum phosphide Same as gas cartridges Same as gas cartridges(Phostoxin, Fumitoxin)

Baiting Chlorophacinone May through June Must be used in bait stations placed around perimeter ofor diphacinone fields or in a grid within fields. Requires multiple feedings.

M E A D OW M I C E

Vegetative Late fall (Oct. to Keep vegetative cover low through dormant periodcover control early Dec.) by mowing or grazing.

Baiting Zinc phosphide Late fall to early spring, Apply before spring breeding, by hand or with a mechanicalbefore alfalfa breaks broadcaster. Do not treat more often than once every 6 months.dormancy Can be used outside field at any time of year.

Chlorophacinone Any time of year Not to be used in alfalfa fields, only along fence rows and surround-or diphacinone ing noncrop areas. Requires multiple feeding. Hand-baiting every

other day for 5 days is recommended.

D E E R A N D A N T E L O P E

Deer fences Must be 8 ft high and made of woven 4-by-4-in. mesh. Almost never worth the expense and effort.

1. Rotation to annual crops is also effective for reducing the population of rodent pests.

v e r t e b r a t e p e s t s 87

teeth, keeping soil out of its mouth while burrowing.Pocket gophers use their short whiskers and tails tohelp navigate tunnels. They seldom travel aboveground; however, they are sometimes seen feeding,pushing dirt out of their burrow system, or moving toa new area. They have a keen sense of smell, whichthey use to locate food. Pocket gophers do not hiber-nate and can be active in the snow. They are moreactive in the spring and fall than they are during theheat of summer. The female usually produces one ortwo litters per year but may produce up to three littersin irrigated alfalfa. Average litter size is 5 or 6 young.Births generally occur from March through June.Pocket gophers have a maximum life span of about 5years.

Pocket gophers are extremely territorial and antiso-cial, living by themselves in an extensive undergroundburrow system that can cover an area from a few hun-dred square feet up to more than 1,000 square feet.Territories are smaller in habitat with abundant food,such as alfalfa fields. Mounds of fresh soil indicatetheir presence. The burrow system may be linear orhighly branched (figure 10.1). A single burrow systemmay be up to 200 yards long. Tunnels are 2 to 3 inchesin diameter and usually from 6 to 12 inches below the

ground, but they may be more than 6 feet deep.Tunnels are usually deeper in sandy soils than in claysoils. One gopher may create several mounds in a dayor as many as 200 mounds per year. Mounds are usu-ally crescent-shaped (figure 10.2) and appear at theend of short lateral tunnels.

Control Methods

A successful pocket gopher control program dependson early detection and control measures appropriateto the location and situation. Most alfalfa growershave relied on poison baits for gopher control. Wherepopulations are low or poison baits have been ineffec-tive, try traps. In a field with a heavy infestation, dragthe field before imposing control measures. Draggingwill enable you to identify active burrow systems.Concentrate gopher control efforts in late winter toearly spring, when the alfalfa is breaking dormancyand before the gophers have given birth. Flood irriga-tion may reduce gopher populations, but it does noteliminate the problem. Rotation to row crops or otherfield crops—such as barley, wheat, oats, rye, or sudan-grass—may help reduce gopher population levels.

Figure 10.1. (left) The burrow system of a single pocketgopher can cover from a few hundred square feet to morethan 1,000 square feet.

Figure 10.2. (below) The pocket gopher pushes soil out of aburrow, creating a crescent-shaped mound; then the gophercloses the hole with a plug.

Toxic baits (rodenticides)h a n d - b a i t i n g Successful hand-baiting dependson accurately locating the gopher’s main burrow. Todo so, use a gopher probe (figure 10.3). Look for thefreshest mounds, because they indicate an area ofrecent gopher activity. You will usually see a small cir-cle or depression representing a plugged lateral tunnel.This plug is generally bordered on one side by soil,giving the mound a crescent shape. Often the mainburrow goes between two mounds. Begin probing 8 to12 inches from the plug side of the mound. When theprobe penetrates the gopher’s burrow, it should sud-denly drop about 2 inches (figure 10.4.). Enlarge theopening the probe has made in the soil by rotating theprobe or inserting a larger rod or stick. Then carefullypour a tablespoon of the bait into the opening. A fun-nel is useful to prevent spillage. Close the probe holewith a rock, clod, or some other material. This willexclude light and prevent soil from falling on the bait.Treat two or three different places in the burrow sys-tem. If gopher activity continues for more than 2 daysafter treatment, treat the burrow again or use anothercontrol method.

Strychnine-treated grain is the most common pock-et gopher bait. Only strychnine bait of 0.5 percent orless may be used for hand-baiting. Anticoagulant baitsare also available for hand-baiting, but they are gener-ally less effective because the gopher must ingest mul-tiple doses over time. All gopher bait is poisonous:Use it with caution. Read and follow product label in-structions carefully.

m e c h a n i c a l b a i t i n g One-time use of amechanical bait applicator (also called a burrowbuilder or gopher machine) can control gophers overlarge areas. This tractor-drawn device (color photo10.2) constructs an artificial underground burrow anddeposits poison-treated grain at preset intervals andquantities. The artificial burrow will intercept most ofthe natural gopher burrow systems. Gophers, by

nature, readily explore these artificial tunnels and con-sume the bait. The percentage of strychnine allowablein mechanical baiting (1.8 percent strychnine) is high-er than that in hand-baiting.

Before using the mechanical bait applicator, deter-mine the depth of existing gopher tunnels by using ashovel. The depth of the burrow builder should be setto that of the existing gopher tunnels. As you createthe artificial tunnel, examine it periodically to makesure that it’s forming properly and that the bait isproperly dispensed (sometimes the applicator tubegets clogged with soil). Proper soil moisture is essen-tial. If the soil is too wet, the tractor will bog downand the tunnel may have an open slot at the top,allowing sunlight to penetrate. If the soil is too dry,the artificial tunnel will cave in, resulting in poor con-trol. Space burrows at 20- to 25-foot intervals. Treatthe perimeter of the field to delay re-invasion fromoutside areas. Use the gopher machine only in areaswhere gophers are present, not as a preventive mea-sure. Gophers seek areas with low resistance to dig-ging; if you build a tunnel where gophers are notpresent, you can actually facilitate their spread. Raise


Figure 10.3. A probe for locating pocket gopher tunnels can be built in a shop. The shaft may be in one piece or divided by pipe coupling forconvenient carrying when it is not in use. (Drawing not to scale.)

Figure 10.4. The probe has entered a main tunnel when the probesuddenly drops about 2 inches. Enlarge the probe hole to insertpoisoned bait.

the shank of the gopher machine out of the groundwhen crossing uninfested areas of the field.

TrappingTrapping can be a safe and effective method to controlpocket gophers when populations are low. It is mosteffective in spring and fall. Several types and brands ofgopher traps are available. A two-pronged pincher trap(such as the Macabee) is the most common. Thegopher triggers it by pushing a flat vertical pan.Another popular trap is the squeeze-type box trap.

As with hand-baiting, trapping requires that youlocate the main tunnel by using a probe. Use a shovelto open the main tunnel, and insert traps in pairs fac-ing opposite directions. This placement will intercepta gopher coming from either direction. A box trap issomewhat easier to set than a pincher trap, but placingit requires more excavation because of its large size.Wire all traps to stakes or flags so you will not losetrack of them or have the trap, with gopher, stolen by apredator. Remember that you will get best resultswhen light is excluded from the burrow. If light entersthe tunnel, the gopher may plug the burrow with soil,filling the traps and making them ineffective. Coverthe opening with soil, sod, cardboard, or some othermaterial. Sift fine soil around the cover to ensure alight-tight seal. Check traps and reset them when nec-essary. Move the traps to a different location if 3 dayselapse without catching a gopher.

Gas cartridgesGas cartridges (smoke bombs) are not recommendedfor pocket gopher control. They are costly and time-consuming and provide variable control. Their ineffec-tiveness may be due to the extensive nature of gophertunnel systems and diffusion of the gas in soil. Because

soil moisture reduces the amount of gas diffusion,treating very moist soils results in better control than treating dry soil.

G RO U N D S Q U I R R E L S

Ground squirrels (Spermophilus spp.) can be seriousproblems. Both California ground squirrels andBelding ground squirrels are found in and aroundintermountain alfalfa fields. California ground squirrelshave a flecked coat and a long bushy tail. In contrast,Belding ground squirrels are slightly smaller, have ashort flat tail, and are solid brown (color photo 10.3).California ground squirrels are generally more of a nui-sance than a serious problem in alfalfa because they pre-fer to stay on field edges, along fence rows or roadsides.However, Belding ground squirrels are a very seriousproblem. They consume large amounts of alfalfa andinhabit the interior of alfalfa fields, constructing mas-sive mounds that can damage hay-harvesting equip-ment. One study estimated that 123 squirrels per acreremoved about 1,800 pounds of alfalfa per acre in 44days. This section pertains primarily to Belding groundsquirrels, not California ground squirrels.

Unlike pocket gophers, ground squirrels are fre-quently visible in the field. They spend much of theirtime out of the burrow, sunning, feeding, or socializing.The burrows provide protection and a place to rearyoung, store food, and rest and sleep. Their burrow sys-tem is not as extensive as that of pocket gophers, but itcan be as deep as 6 feet. Ground squirrel burrow sys-tems are much larger in diameter than are gopher sys-tems, and their burrow entrances are always unplugged.

Belding ground squirrels come out of hibernationand are first visible from mid-January to mid-February. They breed in late February and in March.The breeding season lasts 3 to 6 weeks. Young are bornin the spring. About 4 weeks after birth, the youngsquirrels emerge from the burrow. Females have onlyone litter per year. They may appear to have multiplelitters because the young squirrels are visible for a longperiod, but this is not the case. The fact is that olderfemales breed first and then the younger females breed,thus giving the impression of multiple litters. Littersize ranges from 3 to 12 young and averages about 7young. Females may live 10 years or more and have alife span twice that of males.


Use the gopher machine only in areas where gophers

are present and not as a preventative measure.

When they first emerge after hibernation, the squir-rels may eat nothing at all, surviving on stored fats, orthey may subsist on alfalfa foliage. They prefer greenfoliage in early spring and will not eat seeds like grainuntil later in the season. About June 15 to July 1 someof the adult males go into hibernation for the winter.The adult females begin to hibernate later, and then, asfall approaches, the young born that year begin.Although squirrels are not active for much of the year,they are very energetic and nearly double their bodyweight in a few months.

Control Methods

Deep tillagePreventing excessive populations is much easier thanbringing high populations under control. Therefore,the first step in squirrel management—deep tillage—should occur when an alfalfa field is taken out of pro-duction. Deep tillage is thought to be effective forcontrolling squirrels because it disrupts burrow sys-tems. It is believed to be more effective when done infall than in spring.

ShootingAs a means of controlling large squirrel populations,shooting is seldom effective when used by itself.Shooting is time-consuming, and squirrels becomegun-shy. Shooting is best used for fields with low pop-ulations or to control survivors that remain followingother control operations. Do not approach shootinghaphazardly. Section off the field and systematicallyconcentrate efforts in 1-to 2-acre grids.

Fumigants

AcroleinRegistered in California for the control of burrowingrodents in the spring of 1993, Acrolein (Magnacide) isthe most effective method currently available to con-trol ground squirrels. It has achieved up to 95-percentcontrol of both California and Belding ground squir-rels in field trials and commercial applications. A dis-pensing rod, with nitrogen gas as the propellant,

injects Magnacide into squirrel holes. A Restricted UsePermit from the Agricultural Commissioner’s Office isrequired. Other notification requirements may exist aswell; if so, they will be stated on the permit.Magnacide can be very hazardous. Those who use itmust receive training from company representatives orother qualified persons.

Before using this fumigant, drag the fields to deter-mine which holes are part of active burrow systems.Treat every hole, because distinguishing active burrowsby looking at the location of the holes is impossible.Do not treat burrows until aboveground squirrel activi-ty is apparent. The best time for treatment is early inthe season, after the squirrels become active but before

significant alfalfa growth has occurred. (Alfalfa growthmasks burrow openings, making them difficult tolocate.) Applying the fumigant before the young areborn in the spring is best. Cover holes after treatment.Reopened holes indicate that squirrels were not con-trolled or that the burrow system was invaded byneighboring squirrels. Revisit treated areas to retreatany open burrow systems. If squirrels remain active,burrow systems can be treated after the first cutting.Do not treat holes in the summer or fall; at that timesquirrels start going into hibernation and plug off theirtunnels—rendering Magnacide ineffective.

This fumigant is too costly and time-consuming tobe used on older fields with high squirrel populations.Keep squirrel populations at manageable levels by con-centrating control efforts on young fields or fields withlow infestations.


Keep squirrel populations at manageable levels by concentrating efforts on

young fields or fields with low infestations.

Gas cartridges and aluminum phosphideSmoke bombs and aluminum phosphide (such asPhostoxin and Fumitoxin) have been used with limit-ed success. Although Phostoxin has been effective forcontrol of California ground squirrels, it is only 30 to40 percent effective for control of Belding groundsquirrels. Cold dry soils, which prevent the toxicantfrom penetrating far, may partially explain the poorresults. Also, the burrow system of the Belding groundsquirrel is so extensive that perhaps not enough toxi-cant is released to be lethal.

If you use Phostoxin before March, cold soil willreduce its effectiveness. To determine which holes areactive, drag the field before using gas cartridges orPhostoxin. Gas cartridges are often preferred overPhostoxin because they help the user determine whichholes are part of the same burrow system—smokeescapes from holes in the same system. Seal the holefrom which smoke escapes by stomping on it.Determining which holes belong to the same burrowsystem is difficult when using Phostoxin. Two holesthat are next to each other are not necessarily part ofthe same burrow system, but two holes 25 feet apartmay be. Therefore, you must place Phostoxin tabletsor pellets in every hole.

Baits

Anticoagulant baits (chlorophacinone or diphacinone)have been used in some areas of the IntermountainRegion. Do not use them before May, because squir-rels will not feed on grain early in the season. For baitsto be effective, squirrels must feed on them for at least5 days, with interruptions of no longer than 48 hoursbetween feedings. Greater than 90-percent control hasbeen achieved when anticoagulant baits have beenused properly. Grain baits can no longer be broadcaston fields; they must be used in bait stations (figure10.5). Place bait stations around the perimeter of thefield and within the field at spacings no larger than100 feet.

Squirrel management requires the integration ofseveral control practices, each employed at the correcttime. These practices include deep cultivation in thefall, fumigation with Magnacide, shooting, and anti-coagulant baits.

M E A D OW M I C E

Meadow mice (Microtus spp.)—also referred to asmeadow voles, or field mice—are another seriousrodent pest of alfalfa in portions of the IntermountainRegion. They have been especially problematic inScott Valley and the Tulelake Basin. Meadow mice are4 to 6 inches long when mature. They have heavy bod-ies, short legs and tails, and small, rounded ears. Theirsoft dense fur is blackish brown to grayish brown.

Meadow mice are active all year long. Alfalfa is anideal habitat for them. They feed on all parts of theplant, foraging on stems and leaves in summer and falland roots and crowns in winter and early spring. Theydig short, shallow burrows and make undergroundnests of grass, stems, and leaves. Their presence is indi-cated by well-worn trails, approximately 2 inches wide,leading to entrance holes without mounds (colorphoto 10.4). Their trails are especially evident in latewinter, before the alfalfa resumes growth.


Figure 10.5. This bait station for ground squirrels is made of PVCpipe. Check bait stations on a regular basis to ensure a constantsupply of bait.

Meadow mouse

Spring is the peak breeding period; a second, short-er breeding period occurs in fall. Female meadow micecan produce between two and five litters per year. Anaverage litter contains four or five young. Meadowmouse populations fluctuate dramatically from year toyear, depending on habitat and weather conditions.The populations increase rapidly under favorable con-ditions and the damage they cause can be dramatic.Heavily infested fields can support a population of1,000 to 3,000 meadow mice per acre.

Control Methods

An important component of meadow mouse control ismaking the field and surrounding areas a less favorablehabitat. Controlling weeds and cultivating along fencerows, roadsides, and ditchbanks can help reduce mead-ow mouse populations by reducing the number ofinvading mice. Dense vegetative cover in the fieldencourages meadow mice by providing food and pro-tection from predators and environmental stress.Hence, the amount of alfalfa cover remaining on afield as winter begins affects meadow mouse popula-tions and damage. In areas where meadow mice areknown to be a problem, graze or mow the field in lateOctober to early December, after alfalfa has “frozenback” and is no longer actively growing. This is partic-ularly important in years with snow cover, becausesnow protects meadow mice from predators. Fencescan be constructed to exclude meadow mice, but theyare not cost-effective for protecting alfalfa fields.

TrappingTrapping is not a cost-effective control measure inalfalfa fields, but it is useful to monitor populations.When mouse damage is visible along the edge of afield, set two trap lines of 50 traps each. The numberof mice caught in one night per 100 traps is used toassess the population level. Infestations that yieldfewer than 5 meadow mice per 100 traps are consid-ered light; 10 per 100 traps, moderate; and 20 or moreper 100 traps, heavy. Begin treatment when the popu-lation is moderate.

BaitsToxic baits are necessary where mouse problems areserious. However, at the time of publication, no baitsare registered for use in alfalfa during the growing

season. Zinc phosphide (a restricted-use pesticide) isregistered for use in alfalfa only during the dormantperiod, although it can be used in areas around alfalfafields at any time of year. Treat heavily infested alfalfafields with zinc phosphide (a single-feeding bait) in thelate fall to early spring, before alfalfa breaks dormancyand before mice begin spring breeding. Use a mechan-ical broadcaster to apply bait. Monitor areas aroundthe alfalfa and treat them as needed, at any time ofyear. Zinc phosphide requires only one feeding to belethal. Bait shyness, a condition that results whenmeadow mice consume only enough to make themsick and then discontinue feeding, is a potential prob-lem with zinc phosphide. Follow label instructions tolimit the potential for bait shyness, and do not treatmore often than every 6 months.

Anticoagulant baits may not be used in alfalfa atany time of year, but they can be used at any timealong fence rows and in the surrounding noncropareas. To be effective, meadow mice must consume ananticoagulant over a period of at least 5 days.Therefore, the bait must be available to the mice untilthe population is controlled. The usual procedure is tohand-bait the runways near burrow openings everyother day for 5 days. Read label instructions to ensurethe proper rate of application.

D E E R A N D A N T E L O P E

Deer and antelope can be problematic, consumingsignificant amounts of alfalfa in some fields in theIntermountain Region. Their feeding can be consider-able in fields adjacent to wooded or brush areas.

After obtaining a depredation permit from theCalifornia Department of Fish and Game, you are per-mitted to shoot deer. Shooting is unlikely to solve theproblem, however. Using traps, poisons, and toxic baitto control deer and antelope is illegal. Deer fences arethe only legal, somewhat effective control measure. Afence should be 7 to 8 feet high and made of wovenmesh wire (4- by 4-inch mesh). A few strands ofbarbed wire no more than 4 inches apart can extendthe height of shorter fences. Deer fences are costly andalmost never worth the expense and effort. Damagefrom deer and antelope is largely unavoidable—consider it one of the losses associated with growingalfalfa in the Intermountain Region.



Department of Food and Agriculture. 1986. Vertebrate pest controlhandbook. Sacramento, CA.

Salmon, T. P. 1987. Vertebrate pests of alfalfa.. Proceedings, 20thCalifornia Alfalfa Symposium, 127–38. December 9–10,Visalia, CA.

Salmon, T. P., and R. Lickliter. 1984. Wildlife pest control aroundgardens and homes. Berkeley: University of California Divisionof Agriculture and Natural Resources, Publication 21385.

Salmon, T. P., and R. Marsh. 1981. Vertebrate pests. In M. J.Haley and L. Baker (eds.), Integrated pest management for alfal-fa hay, 32–41. Berkeley: University of California Division ofAgricultural Sciences, Publication 4104.


C H A P T E R E L E V E N

H A RV E S T M A N A G E M E N TSteve B. Orloff and Vern L. Marble

�arvest management is the primary methodby which growers can influence the nutri-tional quality of alfalfa hay, and it has pro-

found effects on forage yield and stand life. Decidingwhen to cut alfalfa is a difficult management decisionbecause the grower must make trade-offs among yield,quality, and stand persistence.

A L FA L FA G ROW T H A N D RO OT R E S E RV E S

To understand the effects of time of cutting, it is help-ful to review some principles of plant growth andalfalfa development. Plants utilize energy from thesun, through the process of photosynthesis, to trans-form carbon dioxide from the air and water from thesoil into carbohydrates (Figure 11.1).

As a perennial plant, alfalfa stores some of the car-bohydrates in its crown and roots. These stored carbo-hydrates are commonly called root reserves. Theyprovide the energy for survival through winter, growthin the spring, and regrowth after cutting. During theseperiods an alfalfa plant pulls carbohydrates from rootsuntil new leaves can photosynthesize carbohydratessufficient to exceed the needs of the growing plant.After cutting, this takes about 2 to 3 weeks, or untilthe alfalfa attains a height of 6 to 8 inches. From this

point the plant begins replenishing root reserves(Figure 11.2). Carbohydrate reserves in roots andcrowns increase with plant maturity until full flower-ing of the alfalfa. Cutting alfalfa at excessively imma-ture growth stages—which occurs when cuttingintervals are very short—does not allow enough timefor the alfalfa to replenish root reserves. Vigor of newgrowth is affected. Stand life may also be reduced ifalfalfa is repeatedly cut before root reserves arerestored.

T H E E F F E C T S O F T I M E O F C U T T I N G

Alfalfa yields per cutting increase as plants mature andthe interval between cuttings increases. Yield increases

103

approximately 120 pounds per acre per day in theIntermountain Region. In theory, the grower shouldobtain maximum yield when alfalfa reaches full bloom(Figure 11.3). Due to leaf aging (senescence) and lossfrom lower portions of mature alfalfa plants, however,the highest yields are sometimes obtained at around50-percent bloom.

In contrast to yield, forage quality declines withadvancing alfalfa maturity (Figure 11.4). Two reasonsexplain this decline. The first involves the proportionof stem weight. During the vegetative stages of alfalfagrowth, the weight of leaves exceeds that of stems.However, as alfalfa matures beyond the early floweringstage, the weight of stems surpasses that of leaves asstems become longer and larger (Table 11.1).Therefore, much of the yield increase after bud stagecan be attributed to increased stem weight, notincreased leaf weight. Since leaves contain more nutri-ents than do stems, forage quality declines. The sec-ond reason why quality declines with maturity is thatthe fiber content of the stem increases as it matures.

In the Intermountain Region, as alfalfa maturesfrom prebud to full bloom, total digestible nutrients(TDN) of a first cutting decline about 1 percentagepoint for every 4-day delay in harvest (that is, adecline of 0.25 percentage points per day). Theamount of crude protein decreases approximately 1percentage point every 5 days.

As mentioned, selecting the proper cutting timeinvolves a compromise between top quality and maxi-mum yield. Longer cutting intervals (that allow thecrop to mature up to 50-percent bloom) generallyresult in higher tonnage and longer stand life butlower-quality hay. Conversely, very high-quality haybut short stand life and lower tonnage usually resultfrom shorter cutting intervals (cutting alfalfa in theearly-bud or prebud stage). In the IntermountainRegion, it takes 3 to 4 weeks to restore root reservesand another 7 to 10 days to add surplus carbohydratesto the roots so the plant is ready for another cutting.Thus, under optimum conditions, the minimum


Cut at bud

Cut at bloom

Full bloom

Budstage

6–8-inchheight

Growthinitiation

Perc

ent r

oot c

arbo

hydr

ate

Figure 11.2. Cutting and growth stage affect the carbohydratecontent of alfalfa roots.

Full-flower PostflowerFirst flowerBudVegetative

Yiel

d

Dige

stib

ility

Stem yield

Leaf yield

Total yield

Forage Digestibility

Figure 11.3. Forage yield relative to quality at different alfalfagrowth stages.

Figure 11.1. Through the process of photosynthesis, plants utilizeenergy from the sun to transform carbon dioxide and water intocarbohydrates. Carbohydrates are used for new growth or are storedin the root for future growth and development. When stored in theroot, carbohydrates are called root reserves.

solarenergy

oxygen

carbon dioxide

cartb

ohyd

rate

s

wat

er

h a r v e s t m a n a g e m e n t 105

interval between first and second cuttings, or secondand third cuttings, is 30 to 50 days. The time dependson weather and alfalfa variety. Regardless of variety,alfalfa will be weakened before the end of the firstgrowing season if cut at intervals of less than 30 days.Too-frequent cutting results in reduced vigor and,often, weed infestation (because root reserves aredepleted, alfalfa plants are less able to compete withunwanted vegetation).

In addition to time of harvest, seasonal changes intemperature and photoperiod (day length) impact for-

age yields and quality. In general, first-cutting forageyields tend to be higher than those of subsequent cut-tings, regardless of the total number of cuttings perseason (Figure 11.5). However, when the first cuttingis taken at a very early growth stage (early-bud orsooner), second-cutting yields may be higher. Thefinal cutting of the season, in the fall, yields less thanprevious cuttings because the alfalfa growth rate hasslowed in response to cooler nighttime temperaturesand shorter day lengths. In contrast to yield, the nutri-tional quality of the fall cutting is typically the highest

6/2850% bloom

7/13100% bloom

6/1810% bloom

6/3Bud

5/29Pre-bud

Yiel

d (to

ns/a

cre)

1.0

0

2.0

3.0

4.0 %crude

protein

%TDN

6025

5520

5015YieldCrude proteinTDN

7/28 8/12 8/27 9/10 9/256/18 6/28 7/136/35/29

Yiel

d (to

ns/a

cre)

1.0

0

2.0

3.0

4.0

Harvest dates

5 cuts4 cuts3 cuts early3 cuts late2 cuts

Figure 11.4. Yield and quality trade-off. As the date of first cuttingis delayed, yield increases dramatically but total digestible nutrients(TDN) and crude protein decrease. (Data were gathered atMcArthur, Shasta County, 1966–69.)

Figure 11.5. Seasonal variation in yield and TDN as they relate tocutting frequency at McArthur, Shasta County, 1966–69.

7/28 8/12 8/27 9/10 9/256/18 6/28 7/136/35/29

Perc

ent T

DN (1

00%

dry

mat

ter)

50

0

55

60

65

Harvest dates

5 cuts4 cuts3 cuts early3 cuts late2 cuts

Table 11.1. Relative proportions of leaves and stems of alfalfa atthree growth stages.

P E RC E N TA G E O FG ROW T H S TA G E L E AV E S S T E M S

Bud stage 63 371⁄10 bloom 48 521⁄2 bloom 46 54

Source: Meyer and Jones (1962)

of the season. Alfalfa harvested in the spring and fallhas higher TDN than alfalfa cut at the same growthstage in midsummer. Therefore, to achieve dairy-qual-ity hay, alfalfa must be cut at a less mature stage inmidsummer than in spring or fall. The yield sacrificeassociated with such early cutting may be significant,encouraging many growers to delay harvest and pro-duce beef or horse hay in midsummer.

S E L E C T I O N O F A C U T T I N G S C H E D U L E

There is no optimum cutting schedule for all growersin all locations in the Intermountain Region. Severalfactors should influence the selection of a cuttingschedule. These include the quality of the hay desired,weather conditions, the anticipated length of thegrowing season, harvest costs, desired stand life, andthe alfalfa market.

The purpose of producing high-quality alfalfa hayis to take greatest advantage of the plant’s nutrientpotential as a livestock feed. Therefore, hay intendedfor use as a maintenance feed for beef cows or for“hobby” horses can be of much lower quality than thatsold to dairies or used to grow weaner calves or year-lings. Hence, the growth stage at which alfalfa is cutshould reflect the intended use for the hay. The dairyindustry is demanding higher and higher quality. Atone time premium hay had 54 percent TDN; thedairy market is now insisting on 55 or even 56 percentTDN (90% dry matter basis). Hay intended for thismarket must be cut early (late-bud stage at the latest)for the necessary quality to be achieved. Conversely,hay intended for beef cattle or horses can be cut later,at 10- to 30-percent bloom, to maximize yields withacceptable quality for these classes of livestock.

Alfalfa fields are sometimes harvested on a calendarbasis, using a fixed interval and a fixed number of cut-tings per season. The advantage of this method is thatthe number of cuttings per season is predetermined.This facilitates planning—it allows advance schedul-ing of irrigation, the cutting of other fields, and otheractivities. The problem with this method is that itdoes not account for weather or dormancy differencesamong alfalfa cultivars. Weather, primarily tempera-ture, has a significant effect on alfalfa developmentand will cause plant maturity on a given date to vary

from year to year. The dormancy of a variety alsoinfluences its development. In general, a less dormantvariety matures more rapidly than a dormant variety.Also, plants from different dormancy classes responddifferently to temperature and photoperiod. Dormantvarieties are more responsive to photoperiod than areless dormant varieties.

Another method of scheduling alfalfa harvests usesthe growth stage of alfalfa to indicate the appropriatetime to cut and the number of cuttings per season. Thegrower selects a specific alfalfa growth stage (such asbud, late-bud, 10-percent bloom, etc.) at which har-vest will begin. This method takes into account theeffects of environmental and varietal differences andresults in more consistent, predictable forage yield andquality than when harvesting on a calendar basis. Insome areas, the alfalfa growth stage at harvest is basedon the appearance of bud or bloom; in others,regrowth from crown buds is used to indicate the prop-er time to cut. The regrowth method is less reliablewith the dormant cultivars produced in the Inter-mountain Region. The primary drawback to cuttingbased on stage of development is that the number ofcuttings per season is not defined—a partial cuttingmay remain at the end of the season. Unless grazing orgreen chopping is an option, there is little a grower cando when 0.50 to 0.75 ton of forage per acre remains inthe field at the end of the growing season.

The relatively short growing season in theIntermountain Region restricts the harvest schedule.Therefore, consider both calendar date and stage ofgrowth when deciding on a harvest strategy. Modifyharvest timing to fit three or four cuttings into the sea-son. Four cuttings are often appropriate in the lower-elevation valleys and where dairy-quality alfalfa is


Much of the yield increaseafter bud stage can be attrib-uted to increased stem weight

not increased leaf weight.

desired for all cuttings. However, the harvest costsimposed by a fourth cutting must be weighed againstany price premiums that may be received for this top-quality alfalfa. A three-cut schedule is usually pre-ferred when at least one cutting is used for beef cattleor horses.

Base the timing of the first cutting on the growthstage of the alfalfa. Cut alfalfa at the growth stage thatwill most likely result in the quality and yield desired.For example, cut at early-bud stage for a 1.5 to 2.5 tonper acre yield of dairy-quality hay, but cut at early-bloom stage for a 2.5 to 3.5 ton per acre yield of haysuitable for nonlactating dairy cows or beef cattle. Ifthe date of the first harvest is very early or very late,regardless of the stage of development of the alfalfa,the calendar date will impact the timing of other cut-tings; the total number of cuttings per season maythen need to be adjusted. Likewise, consider thegrowth stage of the alfalfa and the calendar date whenadjusting the date of cutting to accommodate varia-tion in weather.

In valleys over 4,800 feet in elevation, the choice isnormally between two and three cuttings. Research hasshown that producers obtain equal yields by makingthree cuttings instead of two. However, by makingthree cuttings, they greatly improve forage quality andmarketability.

C U T T I N G H E I G H T

Leave a stubble height of 3 to 4 inches when cuttingalfalfa. Studies from the central and northern UnitedStates have shown that average annual yields of drymatter, protein, and digestible dry matter decrease ascutting height increases from 3 to 9 inches. Maximumyields were obtained at the 3-inch cutting height.Raising the cutting height did increase forage quality,but it caused a significant decrease in production thatmore than offset the slight increase in quality.

FA L L H A RV E S T M A N A G E M E N T

The decision about when to begin the final alfalfa har-vest of the season deserves considerable attention.Although weather conditions and their suitability for

making hay are important, they are not the only crite-ria. Keep in mind the effect of fall harvest manage-ment on stand life and vigor. Fall harvest managementcan also influence winter weed infestation, especiallyinfestation by downy brome (cheatgrass) or hare barley(foxtail).

As mentioned, stored carbohydrates provide theenergy for regrowth after cutting and initial regrowth

in spring. You must allow the alfalfa sufficient time toreplenish root reserves before cutting it. In addition tospring regrowth, root reserves are needed for winterhardiness. Insufficient root reserves going into thewinter can result in reduced vigor, stand loss, andlower yields the following spring. Therefore, the lastharvest of the growing season should occur 4 to 6weeks before the first killing frost. (A killing frost isgenerally believed to be 25º to 26ºF, or –4º to –3ºC.)Cutting after a killing frost does not deplete rootreserves. Consequently, a late harvest or grazing can bemade during late October or early November if fieldconditions permit and growth is sufficient for aprofitable crop. Unfortunately, curing conditions areseldom favorable at this time, so grazing or silage isusually the only option.

Predicting when a killing frost is likely to occur canbe difficult. A grower can only rely on experience andhistorical weather data to time final cuttings. When agrower has numerous fields, cutting them all at theoptimum time may be impossible. Fields cut too closeto the first killing frost (mid-September to mid-October) should be allowed to grow to a late stage ofdevelopment before the first cutting is made the fol-lowing spring. The consequence of not doing so isreduced subsequent yields.

Most alfalfa growers in the Intermountain Region


The last harvest . . . shouldoccur 4 to 6 weeks before the

first killing frost.

have few alternative cash crops and want alfalfa standsto produce for 6 to 8 years or longer. For these grow-ers, fall harvest management is critical. However, ifprofitable rotation crops are available and a stand lifeof only 3 to 4 years is desired, fall harvest managementis much less important.


Marble, V. L., K. G. Baghott, R. W. Benton, P. D. Smith, and R.H. Gripp. 1985. Producing quality alfalfa in California’smountain valleys. Calif. Agric. 39:27–30.

Sheaffer, C. C., G. D. Lacefield, and V. L. Marble. 1988. Cuttingschedules and stands. In A. A. Hanson, D. K. Barnes, and R.R. Hill, Jr. (eds.), Alfalfa and alfalfa improvement, 412–37.Madison, WI: American Society of Agronomy, Crop ScienceSociety of America, and Soil Science Society of America.Number 29.



C H A P T E R T W E L V E

H AY C U R I N G ,B A L I N G , A N DS TO R A G ESteve B. Orloff

� ignificant yield and quality losses occur whenalfalfa is not harvested correctly. The goals ofharvesting are to cut alfalfa at the growth stage

that provides the optimum combination of yield andquality and to maintain quality and minimize lossesthrough rapid curing and timely raking and baling.There is increasing interest in maximizing hay qualitythrough variety selection and management. Theseefforts are nullified if the high-quality alfalfa is notharvested and stored properly.

Nearly all alfalfa in the Intermountain Region isharvested for hay, so this chapter emphasizes hay-making practices rather than those used when makinggreen chop or silage. The hay-making procedure mostcommonly used in the Intermountain Region is afour-step process. It begins with cutting the alfalfa,which is usually done with a 12- or 14-foot self-pro-pelled swather. After a few days the partially dried, orcured, hay is raked to turn the windrow, and twowindrows are combined or laid side by side. This has-tens the curing process and improves the efficiency ofthe baling operation. After the hay has driedsufficiently, it is baled. Finally, it is roadsided by a self-propelled bale wagon.

H AY C U R I N GOne of the most critical aspects of harvesting is dryingcut alfalfa to a point where it can be safely baled. Thisis especially true in the Intermountain Region, wherethunderstorms pose a significant and continual threat.Rapid, uniform curing of alfalfa is highly desired. Itminimizes quality losses due to bleaching, respiration,leaf loss, and rain damage and improves subsequentyields by reducing the effect of windrow shading, less-ening traffic damage to regrowth buds, and allowingtimely irrigation after cutting.

The moisture content of alfalfa growing in the fieldis generally between 75 and 80 percent. The dryingrate of cut alfalfa depends upon several environmentalvariables. These include solar radiation, temperature,relative humidity, soil moisture, and wind velocity.Research in Michigan and California indicates thatsolar radiation is by far the most significant environ-mental factor influencing drying rate.

109

The objective of the hay producer is to utilize man-agement practices that accelerate the drying rate with-in the confines of uncontrollable environmentalconditions. To determine which management prac-tices would be most effective, it is helpful to under-stand the alfalfa drying process.

The drying process of alfalfa occurs in two phases.The drying rate during each phase is governed by theresistance to water loss from the plant (Figure 12.1explains various resistances to moisture loss). The firstphase, or rapid drying phase, accounts for approxi-mately 75 percent of the moisture loss that occurs dur-ing the curing process and requires only 20 percent ofthe total drying time. The stomata (leaf pores) are wideopen, and moisture loss occurs from leaves throughthese openings and from water transfer from the stemsthrough the leaves. Some water also departs throughthe cut ends of stems and through bruised tissue. Themain limiting factor to drying during the first phase isboundary layer resistance, the resistance offered by thelayer of still moist air around the plant. Wind movingover and through the windrow can accelerate dryingby replacing the moist air in the boundary layer withdrier air. The first phase is usually complete before theend of the first day after cutting. The second phase, theslow drying phase, commences at about 40 percentmoisture content, when the pores of the leaf and stemclose. Stomatal resistance increases immensely anddrying rate depends on cuticular resistance. Comparedto moisture loss in the initial phase, moisture loss isextremely slow in this phase. In fact, the drying rate inthis phase is 1⁄100 the initial drying rate.

Mechanical Conditioning

To accelerate curing, many growers mechanically con-dition or crimp the alfalfa as they cut it. In fact,mechanical conditioning has become a widely accept-ed practice. Most conditioners lightly crush the foragebetween intermeshing rollers located behind the head-er of the swather. The primary rationale for crimpingis to crush and break the stems, which dry more slowlythan leaves, thus facilitating water loss and bringingthe drying rate of stems more in line with that ofleaves. Mechanical conditioning affects both phases ofthe drying process. It accelerates the rapid phase bycrushing stems, and it accelerates the slower phase bybreaking the cuticle. Sometimes growers question theeffectiveness of mechanical conditioning and wonderif the cutting operation could be simplified if the con-ditioning rollers were removed. Research has shownthat mechanical conditioning hastens the dryingprocess by as much as 30 percent. Drying time savedby mechanical conditioning can vary considerably,however, depending on weather conditions and alfalfayield. Conditioners should be set so that stems arecracked and crushed but not cut or severely macerat-ed. Consult the owner’s manual for proper condition-er adjustment.

Chemical Conditioning

Chemical conditioning involves the use of a dryingagent, usually potassium carbonate or a mixture ofpotassium and sodium carbonate. A drying agent isapplied during swathing. The chemical hastens the


• Boundary layer resistance: resistance related tothe layer of still moist air close to the plantsurface

• Cuticular resistance: the resistance of theplant surface to water movement

• Stomatal resistance: resistance that is con-trolled by the pores on the surfaces of leavesand stems

Wide windrows often dry one day faster than narrowwindrows . . . more of the

alfalfa is exposed to radiantsolar energy.

Figure 12.1 Resistances to water loss from alfalfa.


drying process by allowing water to pass more freelythrough the waxy cuticle on the plant surface. Thus,drying agents affect the second, or slow, phase of thedrying process. These agents are most effective whenthe weather is warm and sunny. Under poor curingconditions or when there is rain during drying, dryingagents present no advantage. Drying agents have notbecome popular in the Intermountain Region (or inCalifornia as a whole) because of their cost, the needto haul large volumes of water to and through the fieldto apply them, and the good curing conditions inmost of California (compared to those in theMidwest). Therefore, they are not believed to be cost-effective in most situations in the IntermountainRegion.

Swath Management

Wide, airy windrows dry more rapidly than conven-tional ones, which are narrow and dense. This hasbeen demonstrated in several California trials and innumerous trials throughout the United States (Figure12.2). The extent of the advantage that widewindrows offer depends on the geographic area, thetime of year, and the yield level. In general, widewindrows are most beneficial in the spring, whenyields are high and day length is long (that is, there is

more solar radiation than in other seasons). Widewindrows often dry one day faster than narrowwindrows because the forage is spread out and more ofthe alfalfa is exposed to radiant solar energy. Also,because they encounter less boundary layer resistance,wide windrows do not inhibit moisture movement tothe degree narrow ones do. Wide windrows improvethe uniformity of drying, which affects when alfalfacan be raked and baled. The start of these practices isdetermined not by the average windrow moisture con-tent, but by the moisture content of the wettest por-tion of the windrow. Therefore, since the moisturecontent of wide windrows is relatively uniform, theycan be raked and baled earlier. If wide windrows arenot raked earlier, their advantage is lost.

Some growers are reluctant to switch to widewindrows; they fear that, because wide windrowsexpose more surface area to the elements, color lossfrom bleaching will result. However, researchers whohave compared alfalfa from wide and narrow windrowshave not observed any significant color difference.Although wide windrows do expose more alfalfa, theyusually can be raked and baled sooner, so exposuretime is reduced. Also, wide windrows remain wideonly until they have dried sufficiently to rake. Rakingusually occurs after the first drying phase. Littlebleaching occurs during the initial phase, because thewaxy cuticle of the plant is largely intact. During thefinal curing phase, when most bleaching occurs, widewindrows have been raked and combined so they areno wider than raked conventional windrows.

Many growers have not switched to wide windrowsbecause of equipment limitations; the width of condi-tioning rollers and windrow baffles determineswindrow width. Some new swather designs have con-ditioners nearly as wide as the swather header, sogrowers can alter windrow width with a simple adjust-ment of a lever. Fortunately, inexpensive windrowconditioner shields have been developed that modifytraditional swathers so they can spread windrows.

Because of their width, wide windrows must beraked prior to baling and cannot be baled directly outof the swath. Obviously, this is not a problem in areaswhere windrows are always raked. Also, windrowwidth should not be greater than that which can beeasily managed with available rakes.

2 310

Perc

ent M

oist

ure

20

10

30

40

50

60

70

80

Days after swathing (9-ft. wide swath header)

3 ft.4.5 ft.6 ft.

Windrow width

Figure 12.2. The effect of windrow width on alfalfa drying rate.(Source: Klamath Agricultural Experiment Station, Oregon StateUniversity.)

Raking

The purpose of raking is to expedite the drying processby transferring the alfalfa to drier soil and inverting thewindrow. Inversion exposes alfalfa on the bottom ofthe windrow, which at this point has a higher moisturecontent than that at the top. Also, raking usually com-bines two windrows, thus facilitating baling and road-siding. Raking is very effective, but it must be done atthe proper moisture content; otherwise, excessive yieldand quality losses will occur (Figure 12.3). Manygrowers rake alfalfa when it is too dry.

The optimum moisture content for raking is 35 to40 percent. At this moisture content, a significantincrease in drying rate is achieved while severe leaf lossis avoided. Raking at too high a moisture content maytwist (commonly referred to as rope) rather thaninvert the hay and can actually slow drying rate. Leafloss associated with raking hay too dry is significant.When raking hay at 20 percent moisture content, 21percent of leaves are lost; when raking at 50 percentmoisture, only 5 percent are lost (Table 12.1).Therefore, hay raked just prior to baling will be toodry. The greatest loss is in the leaf fraction. Such losssignificantly reduces the quality of the hay, since leavesare its most nutritious component. Research hasshown that raking alfalfa hay that is too dry is moredetrimental to hay quality than baling when too dry.In one study, late raking resulted in a 25 percent loss

in yield and a 2- to 4-percentage unit reduction intotal digestible nutrients (TDN). (Baling when toodry resulted in a 5-percent loss.) If alfalfa was bothraked and baled too dry, the loss increased 10 percentover the raking loss.

B A L I N G A N D S TO R A G E

Alfalfa must be baled within a relatively narrow rangeof moisture content to avoid losses in yield and qual-ity. Whenever possible, refrain from baling hay that isbelow 12 percent moisture, because leaf shatter andloss will be excessive. Hay baled at too high a moisturecontent is subject to problems with mold and dis-coloration. The maximum moisture content for balingdepends on bale size and density. In general, bale smalltwo-tie bales at less than 20 percent moisture, largerand denser three-tie bales at less than 17 percent, and1-ton bales at less than 14 percent. The source ofmoisture within the bale affects the upper moisturelimit for safe baling. Hay can be baled at a highermoisture content when the moisture source is freemoisture (dew) than when it is moisture trappedinside the stem (stem moisture). Free moisture is morereadily dissipated than stem moisture.

Moisture Content Estimates

A simple and practical method to determine if alfalfahay can be safely baled is to grab a handful of alfalfawith both hands and twist it by rotating your wrists inopposite directions. If the stems crack and break, thehay is usually dry enough to bale. The thumbnail testis an even better method. Scrape an alfalfa stem withyour thumbnail. If the epidermis, or outside layer,cannot be peeled back, the hay has dried sufficiently(Figure 12.4). A moisture meter is a valuable tool toevaluate the moisture content of hay. Resistance-typemoisture meters are used as hand probes or mountedon the baler chamber for on-the-go moisture monitor-ing. How dependable are readings from moisturemeters? Researchers have tested their accuracy andfound that their readings were within 2.6 percentagepoints of actual moisture content. Generally, metersindicate a moisture content that is slightly higher than


30 40 5020

Perc

ent y

ield

loss

10

0

20

30

40

Moisture content

LightMediumHeavy

Swath thickness

Figure 12.3. The effect of moisture content and swath thickness ondry-matter losses during raking. (Source: C. A. Rotz, Michigan StateUniversity.)

the actual content. They measure stem moisture lessaccurately than they measure dew moisture.

Moisture for Baling

After alfalfa is fully cured, dew or high relative humid-ity must soften the leaves. Otherwise, excessive leaf losswill occur during baling. Sometimes, mostly in mid-summer, dew or humidity is insufficient for this pur-pose. Delaying the baling operation to wait for dew isundesirable—yield declines and leaf loss increases thelonger hay is left in the windrow. The chance of raindamage also increases proportionately. Additionally,waiting for dew postpones other necessary operations(such as irrigation and cutting of other fields), thus

disrupting the cutting cycle and possibly reducingyield and quality.

Windrows can be sprayed with water to compen-sate for a lack of dew or on days when humidity isinsufficient to permit baling. A three-tier boom setupwith seven hollow cone nozzles is an effective spraysystem (Figure 12.5). Two adjustable hollow conenozzles are mounted on each of the two leadingbooms. The spray angle of these adjustable nozzles isnarrowed to promote water penetration into thewindrow. Three standard hollow cone nozzles aremounted on the trailing boom to mist over the entirewindrow. Water is sprayed on the windrow at the rateof 40 to 50 gallons per acre. Depending on weatherconditions, allow 10 to 30 minutes between waterapplication and baling; this time allows the water topenetrate and soften the leaves. This practice is oftenan acceptable substitute for natural dew, or it can beused to extend the baling period on days with margin-al humidity. However, applying water to windrowsdoes not make midday baling possible. The highevaporation rate at this time negates the effectivenessof spraying.

Moisture Content for Safe Storage

The maximum moisture content for safe hay storage isinfluenced by the uniformity of moisture within bales,climatic conditions during storage, and ventilation atthe storage site. The moisture content of high-mois-ture bales can be reduced somewhat by allowing themto remain in the field until late afternoon; then road-


Figure 12.4. Three methods to evaluate the moisture content of alfalfa hay. (A) The twist method: Grab a handful of alfalfa with both handsand twist it by rotating your wrists in opposite directions. If the stems crack and break, the hay is dry enough to bale. (B) The thumbnail test:Scrape an alfalfa stem with your thumbnail. If the epidermis, or outside layer, cannot be peeled back, the hay has dried sufficiently. (C) Resistance moisture meters: Probe the bale several times and read the meter to learn the moisture content.

(A) (B) (C)

Table 12.1 Yield and leaf loss during harvest operations.

OPERATION YIELD LOSS1(%) LEAF LOSS (%)

Mowing and conditioning 2 3

Raking

At 60% moisture 2 3

At 50% moisture 3 5

At 33% moisture 7 12

At 20% moisture 12 21

Baling, pickup and chamber

At 25% moisture 3 4

At 20% moisture 6 4

At 12% moisture 6 8

Source: Pitt, R. E. 1990. Silage and hay preservation. Ithaca, NY.1. Reported on a 100% dry-matter basis.

side them. Another way to reduce moisture content isto position balewagon loads outside with a gapbetween the stacks before storing the bales in a barn.Unfortunately, these methods are only partially effec-tive; neither method can dissipate moisture deep with-in the interior of bales.

Significant yield and quality losses can occur duringstorage. Studies have indicated dry-matter losses of 1percentage point for each percentage of moistureabove 10 percent. Quality losses can take severalforms. Molds may develop in hay stored at a moisturecontent greater than 20 percent. Molds can producetoxins that reduce palatability and are hazardous tolivestock. Mold respiration causes heating, and, whenhay temperatures exceed 100ºF (38ºC), browningreactions begin. Reactions that occur during brown-ing, coupled with heating from mold growth, cancause temperatures to increase further. Heating mayreduce the protein and energy available to the animalthat consumes the hay (Table 12.2). When bale tem-peratures exceed 150ºF (66ºC), spontaneous combus-tion can occur. This is most likely in hay with amoisture content over 30 percent.

Heating during the first month actually helps dryhay; hence, after the first month, hay has usually driedto a moisture content where it is stable and can bestored safely. Therefore, any problems that result fromstoring hay with an excessive moisture content are mostlikely to occur during the first month of storage.Although the majority of dry-matter losses during stor-age occur in the first month, Rotz (1994) and others


Direction of travel

Front View

Rear View

Figure 12.5. (A) This figure shows a three-tier spray boomconfiguration for adding moisture to windrows. Two adjustable hol-low cone nozzles are mounted on each of the two leading booms.Only two nozzles are mounted on each boom so that the sprays donot intersect and deposit an excessive amount of water where thepatterns overlap. Three standard hollow cone nozzles are mountedon the third boom. (B) As the front-view illustration shows, theboom setup contains a total of four adjustable hollow cone nozzles.Their spray angle is narrowed to promote water penetration into thewindrow. (C) The three standard hollow cone nozzles on the trailingboom mist over the entire windrow. As the rear-view illustrationshows, the two outer nozzles are mounted on drops, with swivels.The swivels are angled in, toward the windrow.

(A)

(B)

(C)

Table 12.2. Problems associated with hay heating.

TEMPERATURE PROBLEM

115º–125ºF When coupled with high moisture, molds (46º–52ºC) and odors develop and decrease palatability.

> 120ºF (49ºC) Heating reduces digestibility of protein, fiber, and carbohydrate compounds.

130º–140ºF Hay is brown and very palatable because of(54º–60ºC) the carmelization of sugars; unfortunately,

nutritional value is reduced.

>150ºF (66ºC) Hay may turn black and spontaneous combustion is possible.

Source: V. L. Marble

found that losses continue at a rate of about 0.5 percentper month for the remainder of the storage period.

Bale Ventilators

A bale ventilator creates a hole through the center of astandard rectangular two- or three-tie bale. The hole isformed by a spear, 8 to 10 inches long, that is mount-ed on the center of the baler plunger face. The spearproduces a 2-inch-diameter hole through the entirebale as the hay is compressed in the chamber.Theoretically, the hole facilitates the dissipation ofmoisture from the bale, preventing spoilage of high-moisture hay (hay with a moisture content up to 25percent). However, tests conducted at Michigan StateUniversity showed no benefit from using a bale venti-lator. The bale ventilator did not reduce hay tempera-ture, dry-matter loss, or moldiness, nor did it improvehay quality or color.

Preservatives

Preservatives are intended to allow storage of alfalfahay baled at moisture contents higher than wouldordinarily be considered safe. They are used on haybaled between 20 and 30 percent moisture. Theadvantages of baling at higher moisture contents arereduced leaf loss and reduced field curing time, whichmay help avoid rain damage.

Hay preservatives are usually applied at baling.Organic acids, primarily propionic acid or propionic-acetic acid blends, are the most common preservatives.

They prevent mold growth and heating losses by low-ering alfalfa pH and retarding the growth of microor-ganisms that cause hay spoilage. One disadvantage ofpreservative use is cost. The required application ratefor propionic acid is 10 pounds per ton for hay with amoisture content of 24 percent or less. For hay with amoisture content from 25 to 30 percent, the rate is 20to 25 pounds per ton. These application rates lead torelatively high expenses. What is more, preservativesare seldom 100 percent effective. The causes of erraticeffectiveness are uneven application and areas of highmoisture content within a bale. (An area of a bale withhigh moisture content is commonly called a slug.) Inaddition, propionic acid is hazardous to skin and eyesand corrosive to farm equipment. Alternatives to pro-pionic acid include microbial inoculants and enzymat-ic products, but their results have been unsatisfactoryin most university-sponsored tests. Most researchersconclude that using a preservative to reduce leaf loss isnot usually cost-effective. Preservative use may bejustified only if the product can be used selectively,when rain is imminent. But, as everyone knows, pre-dicting rain can be very difficult.


Dougherty, C. T. 1987. Post-harvest physiology of forages.Proceedings, American Forage and Grassland Conference.

Meyer, J. H., and L. G. Jones. 1962. Controlling alfalfa quality.California Agricultural Experiment Station Bulletin 784.

Orloff, S. B. 1988. Artificial dew to improve baling: Can you beatmother nature? Proceedings, 18th California AlfalfaSymposium, 137–43. December 7–8, Modesto, CA.

Pitt, R. E. 1990. Silage and hay preservation. Ithaca, NY: NortheastRegional Agricultural Engineering Service. NRAES-5.

Rotz, C. A. 1993. An evaluation of hay drying and harvesting sys-tems. Proceedings, 23rd California Alfalfa Symposium, 39–48.December 7–8, Visalia, CA.

Rotz, C. A., and R. E. Muck. 1994. Changes in forage qualityduring harvest and storage. In G. C. Fahey, Jr. (ed.), Foragequality, evaluation, and utilization, 828-68. Madison, WI:American Society of Agronomy, Crop Science Society ofAmerica, and Soil Science Society of America.


When bale temperaturesexceed 150ºF, spontaneous

combustion can occur. This is most likely in hay with a moisture content

over 30 percent.

C H A P T E R T H I R T E E N

Q U A L I T Y A N D Q U A L I T YT E S T I N GSteve B. Orloff and Vern L. Marble

�lfalfa hay grown in the Intermoun-tain Region has a well-deserved reputation for high quality. It is

marketed locally and throughout much of California,in other states, and internationally. Producers recog-nize the importance of growing high-quality hay.Quality has a profound effect on animal performanceand milk production and, consequently, the value andprice of alfalfa hay.

W H AT I S Q U A L I T Y ?

Forage quality is a relative term. What is consideredhigh-quality alfalfa depends on one’s perspective(whether one is the buyer or seller), on current marketconditions, and, most importantly, on the intendeduse for the alfalfa. From a nutrition perspective, foragequality relates to the feeding value of the hay, or theability to convert hay into milk, meat, and fat. Foragequality is a function of both forage intake anddigestibility. As forage quality increases, feed intakeand digestibility increase.

Like all living organisms, alfalfa plants are com-posed of cells (Figure 13.1). Alfalfa cells consist of thesoluble and highly digestible contents of the cell (pro-

tein, sugars, fats, starch, and pectins) and the lessdigestible, structural parts of the cell wall (cellulose,hemicellulose, and lignin). Cell wall content is themost important factor affecting forage utilization and,thus, forage quality. Fiber analyses can indicate the cellwall content of alfalfa hay (fiber analyses are discussedlater in this chapter).

Low-quality alfalfa has a high proportion of cellwall material, and the cell walls are composed of a rel-atively large amount of indigestible compounds, suchas lignin. Lignification of the cell wall, which occurs asalfalfa plants mature, is the primary factor limitingforage digestibility. High-quality alfalfa, in contrast tolow-quality alfalfa, has less cell wall material, and thecell walls are thinner and contain less cellulose andlignin. Not only is high-quality alfalfa more nutri-tious, but it is also more palatable and digestible.Therefore, animals consume it in larger quantities.

117

Q U A L I T Y R E Q U I R E M E N T S

Forage quality needs depend on livestock class—thatis, whether the consumers are high- or low-producingdairy cows, or beef cattle, or ruminant versus non-ruminant animals. High-producing dairy cows requirehighly digestible, high-energy, high-protein forage.Milk output from dairy cows fed low-quality alfalfahay will never equal milk output from cows fed high-quality hay. Compared to high-quality alfalfa, low-quality alfalfa remains in the ruminant digestive tractlonger; this results in decreased intake and animal pro-ductivity. Supplements can only partially compensatefor low-quality hay in the diet. Compared to high-producing dairy cows, low-producing cows, nonlac-tating cows (dry cows), and beef cattle have lowernutrition requirements; they do not require top-quality alfalfa. Similarly, horses (especially inactive“hobby horses”) have lower energy requirements thando lactating dairy cows. In fact, horses can becomecolicky when fed alfalfa of too high a quality. Unlikeruminants, horses can respond to eating low-qualityhay by increasing their consumption of it and passingit through their digestive system more rapidly; thisresponse compensates for the low quality. The primarycriterion when judging alfalfa hay for horses is not its

energy value but its condition. Hay for horses shouldbe free of dust, mold, and weeds.

FA C TO R S A F F E C T I N G Q U A L I T Y

Numerous factors, both controllable management factors and uncontrollable environmental factors,influence alfalfa hay quality. Unfortunately, alfalfaquality and yield are usually inversely related. In otherwords, factors that result in high yields usually resultin decreased forage quality; conversely, factors thatdecrease yield increase forage quality.

Harvest management and variety selectionStage of maturity at the time of cutting is the mostimportant controllable factor (see chapter 11).Quality declines with advancing alfalfa maturity.However, yields increase with advancing maturity, soharvest management is a compromise between maxi-mum yields and maximum quality. Alfalfa varietyselection influences forage quality (chapter 3), as dohay-making practices (chapter 12). Raking or balingwhen the hay is too dry results in excessive leaf shatterand reduced quality. Heating and mold growth occursin hay that is baled too wet. Although quality differ-ences among alfalfa varieties are not great comparedwith differences in other characteristics, most alfalfaseed companies are making a major effort to improveforage quality through breeding. When available, vari-eties that are higher in quality may increase manage-ment options, but they will not replace the need forsound cultural practices.

Seasonal effectsSeasonal variations in light, moisture, temperature,and photoperiod (day length) all affect forage quality.Alfalfa harvested in the spring, or late summer or fall,has a higher leaf and protein content than summer-produced alfalfa of the same maturity. Therefore, thequality of the last hay cutting (third or fourth) is typi-cally the highest of the year. The first cutting produceshigher quality than midsummer hay cutting(s).

Soil moistureEither too much or too little water can impact yieldand quality; however, the relationship is not clear-cut.The usual effect of drought stress is a stunted plant


Figure 13.1. Diagram of a plant cell showing cell wall structure andcell components. (Courtesy Pioneer Hi-Bred International, Inc.)

Primary wall

Secondary wall

Cell wall

Acid detergent fiber (ADF)

Neutral detergent fiber (NDF)

Cell Contents• Proteins• Sugars• Fats• Starch• Pectins

Primary wall

Secondary wall Hemicellulose

Lignin

Cellulose

q u a l i t y a n d q u a l i t y t e s t i n g 119

that, compared to unstressed plants, is leafier, has finerstems, and less fiber, and is more digestible. However,the effect of drought stress on forage quality maydepend on the severity and timing of the stress. Severestress may result in leaf loss and a reduction in quality.At any rate, the yield reduction incurred from mois-ture stress (see chapter 4) is too great a price to pay forhigh-quality hay. Soil type also affects forage quality,but it is difficult to distinguish the effects of soil typefrom its indirect effect on water-holding capacity, soilaeration, and nutrient availability. In general, alfalfaproduced on very fine-textured clay soils or salty soilsis shorter, finer stemmed, and leafier than alfalfagrown on loam or sandy soils.

PestsInsects, diseases, and nematodes can either increase or decrease forage quality, depending on the type ofdamage they inflict. Pest pressures that delay alfalfadevelopment typically result in higher forage quality,but they reduce yields. Some diseases and nematodesmay retard plant growth and yield, resulting inimproved quality. On the other hand, some pestscause a reduction in the leaf-to-stem ratio, an increasein fiber concentration, or a reduction in protein con-centration. All these changes lower feeding value. Forexample, leaf and quality loss is often associated withinsect feeding and disease pressure. The presence ofweeds in alfalfa hay almost always reduces forage quality because most weeds are less palatable andnutritious than alfalfa.

RainfallLike environmental factors, weather conditions afteralfalfa is cut influence quality. Rain is a continualthreat in the Intermountain Region. Rainfall candecrease forage quality considerably—it can shatterand destroy leaves, leach soluble nutrients, and pro-long respiration. The force of raindrops hitting dryingalfalfa disconnects leaves from the stem. The wettingand drying process increases the potential for leaf shat-ter. Rain-damaged alfalfa can be brittle after drying, soit is more susceptible to loss during raking or baling.Extra operations may also be necessary to dry therewetted alfalfa, and these may increase mechanicallosses and reduce forage quality.

Leaching of soluble nutrients is the primary causeof quality loss. Rain leaches the more soluble, highly

digestible nutrients from alfalfa. It leaches some of thesoluble protein and reduces the digestibility of theremaining protein. As a result, rain damage decreasesdigestibility and increases fiber concentration. Rainfallcan cause additional losses by prolonging respiration.After it is cut, alfalfa continues to respire until itsmoisture content drops to less than 40 percent. Rainrewets the forage and allows respiration to continue.

The effect of rain on alfalfa quality depends on theamount, intensity, and duration of the rain as well asthe moisture content of the alfalfa at the time of rain-fall. Leaching losses increase as the amount and dura-tion of rainfall increase. An intense rain for a shorttime has less effect on forage quality than the sameamount of rain over a longer duration. Both leachingand leaf loss are greater with drier alfalfa than withthat which is freshly cut. Rain early in the dryingprocess causes little loss: The cuticle, or outer coatingon the plant surface, is largely intact soon after cuttingand is believed to shed water better at that point thanwhen the forage has dried.

Because of these variables, it is difficult to predictthe quality of rain-damaged alfalfa hay. Just becauserain falls on cut alfalfa does not mean that it is unsuit-able for the dairy market. Rain often has a greatereffect on the visual appearance of hay than on itsnutritional value. Chemically analyze rain-damagedhay to determine its suitability for dairy cows; do notrely on its visual appearance.

H AY E VA L U AT I O N

The ultimate test of hay quality is animal performance.However, an estimate of alfalfa forage quality is usuallyneeded before hay is sold or used as feed. Therefore,alfalfa hay quality is estimated using sensory or labora-tory analysis. Laboratory evaluation may includeeither chemical analysis (“wet” chemistry) or near-

Sampling . . . is the primary factor affecting theaccuracy of quality analysis.

infrared reflectance spectroscopy (NIRS). Often, bothsensory and laboratory analyses are used to evaluatealfalfa hay quality.

Sensory AnalysisThe visual and physical properties used to evaluatealfalfa hay quality include stage of maturity, leafiness,presence of foreign material, condition, odor, color,and texture.

MaturityAs mentioned in the chapter on harvest management(chapter 11), the stage of maturity when alfalfa is cutis probably the single most important determinant ofquality. However, it is difficult for a buyer or broker todetermine the maturity of alfalfa once it has beenbaled. Usually only the presence or absence of bloomcan be determined, and this is an inadequate means bywhich to assess maturity.

LeafinessVisual inspection involves estimating the leafiness ofhay. This is important because leaves are the hay’smost nutritious component. On a 100-percent dry-matter basis, leaves contain 27 percent protein and 70percent total digestible nutrients (TDN); stems at the10 percent bloom stage contain only 13 percent pro-tein and 45 percent TDN. Leafiness is a function ofthe alfalfa maturity, variety, weather, and conditionswhen the hay was raked and baled.

Foreign MaterialA sensory inspection involves assessing the presenceand amount of foreign material. Foreign material maybe weeds, straw, soil, wire, or anything other thanalfalfa. Foreign material may be unpalatable or evenphysically damaging or toxic to livestock. Pay particu-lar attention to unpalatable or toxic weeds (such asfoxtails, yellow starthistle, and fiddleneck), since stan-dard laboratory tests do not detect them.

Condition and odorDusty hay with excessive leaf shatter results from bal-ing with too little moisture. If hay is moldy, or off-color or has an objectionable odor, its moisturecontent was too high for baling.

ColorMany people judge alfalfa hay based on its color. Thegreener it is, they think, the higher its quality. Thesepeople give color too much importance; it is not agood indicator of digestibility. Color merely indicatesthe curing conditions and whether the hay was put upproperly.

TextureSome hay is excessively rough, or “pokey”; other hay issoft and fine textured. Rough-textured hay can beunpalatable and cause intake problems. In severe cases,it can even cause mouth lesions (particularly in horses).

A visual analysis consists of looking at a whole baleor pulling apart a bale and examining hay flakes. Bothvisual and laboratory evaluation of hay quality areimportant (Table 13.1) and should be used in combi-nation. Visual inspection is especially useful to detectweeds, mold, and foreign material—all of which can-not be accurately assessed by chemical analyses. Visualinspection is particularly important when purchasinghorse hay, since horses are especially sensitive to moldand dust.


Table 13.1. Relative reliability of visual inspection and chemicalanalysis for evaluating alfalfa quality.

R E L AT I V E R E L I A B I L I T Y

QUA L I T Y V I S UA L C H E M I C A LFA C TO R I N S P E C T I O N A N A LY S I S

Stage of maturity Poor Excellent

Leafiness Fair Excellent

Foreign material Excellent Poor

Condition Excellent Poor

Green color Excellent Poor

Texture Excellent Poor

ADF and TDN values presented on a laboratory

report should not be considered separately; TDN

is calculated from ADF.

Although visual evaluation is useful for describingthe physical attributes of alfalfa hay, it cannot be usedto estimate the feeding value. Chemical analysis canprovide the information necessary for balancingrations and predicting animal performance.

Laboratory Analysis

Much of the alfalfa hay produced in the Inter-mountain Region undergoes laboratory analysis toestimate its nutritional quality prior to being sold.Values obtained from laboratory analyses are oftenused to set the price of alfalfa hay. The price differen-tial between “dairy-test” hay and “nontest” hay is usu-ally significant. Therefore, results from quality analysesare extremely important to both the dairy and the hayproducer.

Sample Collection

The first step in laboratory analysis is collecting a rep-resentative sample. The importance of proper sam-pling cannot be overemphasized, since it is the primaryfactor affecting the accuracy of quality analysis. Thevalidity of the testing program rests on obtaining arepresentative sample that accurately reflects the qual-ity of the entire lot of alfalfa hay.

Quality differences should not result from differ-ences in sampling methods. When sampling, use a cor-ing device rather than an entire flake of hay or a “grabsample.” Several core samplers are available for alfalfahay (Figure 13.2). The inside diameter of the coringdevice must be no less than 3⁄8 inch and no more than 3⁄4inch. The shaft must be long enough to sample at least12 to 18 inches into the bale. The complexity of coringdevices varies widely. A sampler can be a simple shaft,


Figure 13.2. Representative coring devices for sampling alfalfa hay bales: (A) Penn State forage sampler, (B) Techni-Serv E-Z Probe, (C) sharp-ened golf club shaft, (D) Utah hay sampler, (E) Hay Chec hay sampler, and (F) Forageurs hay sampler.

such as a segment of a golf club or ski pole, or a sophis-ticated device with a sample collection box. (If you usea golf club or ski pole as a sampler, be certain the insidediameter of the shaft is no less than 3⁄8 inch; many arenarrower.) A list of commercially available samplers,their descriptions, and the address of the manufacturercan be found in University of California (UC) Leaflet21457, Testing Alfalfa for Its Feeding Value.

In a test of sampler effectiveness, hay from the samelot was sampled with three different sampling devices.The resulting analyses showed no difference in dry

matter or fiber content. The consistency of the findingsindicated that none of the three sampling devices over-or underselected any component of the hay. Similarly, arecent test in the Intermountain Region indicated thata sharpened golf club shaft, a Penn State forage sam-pler, and a Utah hay sampler were equally effective atproviding representative samples. However, an auger,or corkscrew-type coring device, selectively sampledleaves over stems. This resulted in analysis of TDN thataveraged three percentage points higher than analysis ofsamples taken by other coring devices. A large quantityof fines in the sample bag usually indicates that the cor-ing device selectively samples leaves.

Quality can vary considerably from bale to bale andeven within the same bale. Therefore, to obtain a rep-resentative sample, core a minimum of 20 randomlychosen bales per lot—coring 30 to 40 bales would be


Figure 13.3. (A) Probe the end of at least 20 bales, centering thecoring device in each one. Insert the probe horizontally, 12 to 18inches deep. (B) Store the entire sample in a sealed polyethylenefreezer bag so the laboratory can determine the “as received” mois-ture content.

(A)

(B)

Figure 13.4. Guidelines for taking core samples of alfalfa hay.

• Sample a single lot of hay—that is, hay fromthe same cutting, variety, field, stage of matur-ity, and harvested within a 48-hour period. Alot should not exceed 200 tons of alfalfa.

• Sample at random. Walk around the entirestack and sample bales at various heights.

• Per lot, sample a minimum of 20 bales (onecore per bale).

• The coring device must be a sampling tube, orprobe, with the inside diameter of the cuttingedge at least 3⁄8 inch and no more than 3⁄4 inch.The cutting edge should be flat, not angled.Keep the cutting edge sharp.

• Probe bale ends near the center, horizontally,at least 12 to 18 inches into the bale. Theprobe should enter horizontally at a rightangle to the surface of the end of the bale. Besure the probe does not slant up, down, orsideways.

• Combine core samples into a single sample bystoring them in a sealed polyethylene freezerbag. Storing them in plastic will allow labora-tory technicians to determine the “as received”moisture content.

• The sample should weigh approximately 1⁄2 pound.

• Do not expose the sample to heat or directsunlight and send to a lab as soon as possible.

http://anrcatalog.ucdavis.edu/InOrder/Shop/ItemDetails.asp?ItemNo=21457

better. Probe the stack or lot at various heights andlocations around the stack. Probe a bale near the centerfrom either end, inserting the probe horizontally andperpendicular to the surface of the bale (Figure 13.3).Place all samples into one polyethylene freezer bag andseal it so laboratory technicians can determine the “asreceived” moisture content. Do not divide or subsam-ple prior to grinding; doing so could bias the results ifthe subsample is taken from the top (where there maybe fewer leaves) or bottom (where leaf pieces may set-tle). Take care not to leave the samples on the dash ofyour pickup or any other place where they might besubjected to heat or direct sunlight. Send samples tothe lab as soon as possible after collection. Figure 13.4summarizes sampling guidelines.

Testing

Forage quality can be determined either by chemicalanalyses or by near-infrared reflectance spectroscopy(NIRS). Remember, both methods are only tools topredict animal performance. NIRS is gaining popular-ity because it is fast and accurate. In chemical analysis,or “wet” chemistry, the alfalfa sample is treated withvarious chemicals to destroy or isolate certain plantconstituents. The remaining plant residues are quan-tified and used to estimate the feeding value of thealfalfa. The relationship between chemical analysis andanimal performance has been established throughyears of animal-feeding trials.

Figure 13.5 lists the various laboratory analyses thatare often performed on alfalfa hay. In addition, the fig-ure describes values used to determine quality. Theanalyses normally conducted to evaluate alfalfa qualityin California include moisture, crude protein (CP),and acid detergent fiber (ADF) tests. Total digestiblenutrients (TDN) and other predictions of energy arecalculated by using the ADF value. Many nutritionistsare increasingly interested in neutral detergent fiber(NDF) analysis, which is useful for predicting intake.

m o i s t u r e The water content of hay can vary considerably, depending on the environment and the length of time since harvest. Moisture contentcan have a significant effect on the economic value ofthe hay on a per-pound basis. The price of hay with ahigh moisture content should be discounted accord-ingly. To prevent confusion, laboratories usuallyreport the quality of the hay on an “as received” basis

Figure 13.5. Laboratory analyses to determine the quality of alfalfa.

Crude protein (CP) Estimate of protein based onmeasurement of both protein and nonproteinnitrogen.

ADF-nitrogen (ADF-N) When alfalfa is damagedby excessive heating, a portion of the crude pro-tein becomes bound and is not available to theanimal. The bound protein, calculated from ADF-nitrogen, can be subtracted from the crude proteinto estimate the amount of available protein.

Acid detergent fiber (ADF) Measurement of theplant fiber that remains (cellulose and lignin) afteran acidic detergent removes more digestible cellcomponents. As ADF increases, the digestibility ofalfalfa decreases. ADF is used to calculate many ofthe energy values that appear in hay analysisreports (TDN, DDM, NEL).

Total digestible nutrients (TDN) Calculated fromADF and used to estimate the energy value of for-age. Sum of all digestible organic nutrients (pro-teins, fiber, fat, nitrogen-free extract). TDN is themost extensively used forage quality value inCalifornia for hay-marketing purposes.

Digestible dry matter (DDM) Similar to TDN.DDM is another value calculated from ADF and isan estimate of the energy available in forages. It isused to formulate rations.

Net energy for lactation (NEL) The net energy forlactation is now used more commonly than TDNin dairy ration formulation. It is calculated directlyfrom ADF.

Neutral Detergent Fiber (NDF) This is the fiberthat remains after using a neutral detergent toremove the cell contents and pectin. NDF valuediffers from ADF value in that it includes hemi-cellulose. NDF analysis is considered to be moreuseful for predicting intake; the higher the NDF,the lower the intake.

Relative feed value (RFV) Estimates overall foragequality, combining estimates of both digestibilityand intake (ADF and NDF). This value is notcommonly used in the West.

Calcium (Ca) and phosphorus (P) The quantity ofCa and P, as well as the Ca:P ratio, is important indairy rations. Alfalfa is a good source of Ca but arather poor source of P. Knowing the Ca and Pconcentration in the hay can assist in proper rationformulation.

as well as on a 90- and 100-percent dry-matter basis(Figure 13.6).

c r u d e p r o t e i n CP is measured by determiningthe concentration of nitrogen in the forage sampleand converting this figure to protein by multiplyingby a factor of 6.25 (the factor derives from the factthat plant protein is generally 16 percent nitrogen).Therefore, CP is not just a measurement of protein—it reflects the presence of other nitrogen-containingcompounds, such as amino acids and chlorophyll.Although some laboratories calculate a CP value basedon the fiber content of the hay, fiber concentration isa poor indicator of CP. It should not be used in placeof the standard method: determining the nitrogenconcentration. When alfalfa has been baled withexcessive moisture and heat damage occurs, some ofthe protein may become chemically bound andunavailable. In this case, an analysis for crude proteinwould overestimate the amount of available protein.An ADF-N analysis (see Figure 13.5) is needed todetermine the protein that is unavailable for digestion.

a c i d d e t e r g e n t f i b e r The energy value ofalfalfa hay must be determined indirectly, from itsfiber content. Therefore, the ADF and TDN valuespresented on a laboratory report should not be con-sidered separately; TDN is calculated from ADF. Thehigher the fiber, the lower the energy value. The mostcommon fiber test is ADF analysis, which has largelyreplaced the modified crude fiber (MCF) method formerly used in California. The ADF test is pre-ferred over the MCF method because it is faster, easi-er to run in the laboratory, as accurate as MCF forpredicting TDN, and more accurate than MCF forpredicting the quality of alfalfa-grass mixtures. TheADF test is the method approved by the NationalForage Testing Association. ADF can be converted toTDN by using Table 13.2 or the following equation:

TDN % = 82.38 – (0.7515 x ADF %)

In this equation, all constituents are expressed on a100-percent dry-matter basis. The results of a test canbe expressed as the percentage of dry matter in thesample—90 percent or 100 percent, whichever isdesired. However, the percentage must be specified toavoid confusion. To convert TDN at 100 percent drymatter to TDN at 90 percent dry matter, multiply by

0.90. Conversely, to convert TDN at 90 percent drymatter to TDN at 100 percent dry matter, divide by0.90 (or multiply by 1.11).

Consistency of Results

Growers, brokers, and dairy producers have been frus-trated by variability in laboratory results. Confusionhas arisen due to different analysis procedures amongregions, states, and individual laboratories. TDN values have varied, although the digestibility of the for-age has been the same. Some states and laboratorieshave used different procedures to determine ADF and


Table 13.2. Relationship between acid detergent fiber (ADF) andtotal digestible nutrients (TDN) at 100 and 90 percent dry matter(DM).

% A D F % T D N

1 0 0 % D M 9 0 % D M 1 0 0 % D M 9 0 % D M

20.0 18.0 67.4 60.7

21.0 18.9 66.6 59.9

22.0 19.8 65.8 59.2

23.0 20.7 65.1 58.6

24.0 21.6 64.3 57.9

25.0 22.5 63.6 57.2

26.0 23.4 62.8 56.5

27.0 24.3 62.1 55.9

28.0 25.2 61.3 55.2

29.0 26.1 60.6 54.5

30.0 27.0 59.8 53.8

31.0 27.9 59.1 53.2

32.0 28.8 58.3 52.5

33.0 29.7 57.6 51.8

34.0 30.6 56.8 51.1

35.0 31.5 56.1 50.5

36.0 32.4 55.3 49.8

37.0 33.3 54.6 49.1

38.0 34.2 53.8 48.4

39.0 35.1 53.1 47.8

40.0 36.0 52.3 47.1

At 20 core samples per lot, the standard error is typicallyone percentage point of TDN.

Lab Name

Address

Sample No.: ______________________________

Date received: ______________________________

Date sampled: ______________________________

Date reported: ______________________________

Name: ______________________________ Lot I.D.: ______________________________

Address: ______________________________ Lot size: ______________________________

______________________________ Cutting number: ______________________________

I. Laboratory Analyses:

Dry matter (DM), %Acid detergent fiber (ADF), %Crude protein (CP), %

II. Estimated Energy Values (calculated from ADF)

Total digestible nutrients (TDN), %Net energy for lactation (NEL), Mcal/lbDigestible dry matter (DDM),%

III. Hay Quality Rating for This Sample (ADF values on a 100% DM basis)

■■ Premium (29.0% ADF or less) ■■ Fair (32.1 to 37% ADF)■■ Good (29.1 to 32% ADF ■■ Low (more than 37% ADF)✔

even different mathematical equations to predict TDNfrom ADF. TDN values reported from laboratoriesusing different methods are not interchangeable.Details of the recommended system for California areprinted in UC Leaflet 21457, Testing Alfalfa for ItsFeeding Value. Confusion has also occurred becauseforage quality values have been reported at differentpercentages of dry matter. Some of this confusion canbe avoided if the alfalfa industry focuses on the ADFvalue rather than the predicted TDN and if labs reportresults on an “as received” 90-percent and 100-percentdry-matter basis.

Differences among laboratories do exist, but thesecan be minimized by following standard sampling and laboratory procedures. Remember, when splittinga sample to send to two laboratories, grind and mix thesample prior to dividing.

The National Forage Testing Association (NFTA),

composed of researchers, extension specialists, haydealers, and commercial forage-testing laboratories,sponsors a voluntary laboratory certification programto improve the consistency of laboratory results andreduce discrepancies that occur between laboratories.Guidelines for standardized sampling, analysis, andreporting are available. Participating laboratoriesreceive a ground alfalfa sample for analysis once every3 months. A laboratory is certified when its results fallwithin an acceptable range for three out of the fourannual samples. Using a certified laboratory can helpensure the reliability of the forage quality analysis.

What are typical forage quality values? Table 13.3lists expected ranges of alfalfa forage quality. Knowingexpected ranges of CP, ADF, and TDN for alfalfa atdifferent maturity levels helps a grower assess the credi-bility of laboratory results. If reported values fall toofar from anticipated values, consider disregarding the


Figure 13.6. A hay quality analysis form as provided by a laboratory.

Dry Matter BasisAs received 90% DM 100% DM

85.5 90.0 100.024.7 26.0 28.918.6 19.6 21.8

51.9 54.6 60.70.530 0.558 0.620

56.8 59.8 66.4

John Haygrower2215 Ranch LaneHigh Mountain, CA

01066/10/946/7/946/13/94

Field 4B120 tonsOne



results or resubmitting samples for another analysis atthe same or a different laboratory.

Limitations of Laboratory Testing

Growers, brokers, and dairy producers should be awareof the limitations on the degree of accuracy that can beachieved with hay quality analysis and not put toomuch weight on absolute values. For example, there isprobably no difference in quality between hay thattests 54.7 and 55.2 percent TDN. Analytical methodsare not accurate enough to detect such small differ-ences. Variability exists in the lab results, both with“wet” chemistry and with NIRS analysis; however, thegreatest loss in accuracy occurs with sampling. Theissue is how well a sample represents the entire lot ofhay. At 20 core samples per lot, the standard error istypically one percentage point of TDN. If fewer sam-ples are taken, the error is considerably more. Thisunderscores the need to obtain a representative sample.

Quality testing for forage has advanced significantlyin the last decade, and quality analysis is a useful toolfor determining the nutrition quality of alfalfa hay and assessing its value. However, growers, brokers, and

dairy producers must realize the limitations of forageanalysis. Whenever possible, they should assess thevalue of hay by judging its effect on animal perfor-mance, as well as using sensory and chemical tests.


Bath, D. L., and V. L. Marble. 1989. Testing alfalfa for its feedingvalue. Oakland: University of California Division ofAgriculture and Natural Resources, Leaflet 21457.

Fahey, G. C., Jr., ed. 1994. Forage quality, evaluation, and utiliza-tion. Madison, WI: American Society of Agronomy, CropScience Society of America, and Soil Science Society ofAmerica.

Hannaway, D. B. and P. J. Ballerstedt. 1988. Testing the quality ofalfalfa hay. Oregon State University Extension Service. PNW223.

Holland, O., and W. Kezar, eds. 1990. Pioneer forage manual: Anutritional guide. Des Moines, IA Pioneer Hi-BredInternational.

Mueller, S. C. 1992. Production factors affecting alfalfa hay quality.Proceedings, 22nd California/Arizona Alfalfa Symposium,84–97. December 9–12, Holtville, CA.


Table 13.3. Expected ranges of alfalfa forage quality at various growth stages.1

1 0 0 % D RY M AT T E R 9 0 % D RY M AT T E R

G ROW T H S TA G E D E S C R I P T I O N % C P % A D F % T D N % C P % A D F % T D N

Prebud >12 in. long, no buds or flowers 25.0–29.0 21.0–25.0 63.5–66.5 22.5–26.0 19.0–22.5 57.0–60.0

Early bud 1–2 nodes with buds, no flowers 22.5–26.0 24.5–28.5 61.0–64.0 20.0–23.5 22.5–25.5 55.0–57.5

Late bud >3 nodes with buds, no flowers 20.5–24.0 27.0–30.5 59.5–62.0 18.5–21.5 24.5–27.5 53.5–56.0

Early bloom 1–15% bloom 18.0–22.0 29.0–35.0 56.0–60.5 16.0–20.0 26.0–31.5 50.5–54.5

Midbloom 16–85% bloom 15.5–20.0 34.0–37.5 54.0–57.0 14.0–18.0 30.5–34.0 49.0–51.0

Full bloom 86–100% bloom 14.0–17.0 36.5–40.0 52.5–55.0 12.5–15.5 33.0–36.0 47.0–49.5

1. Values are rounded to the nearest 0.5 percent.

C H A P T E R F O U R T E E N

G R A Z I N G M A N A G E M E N TRhonda R. Gildersleeve

� razing, as an alternative to hay or silage pro-duction, has not been widely promoted in theUnited States until recent years. Generally,

alfalfa does not persist well under continuous grazingconditions. Although using alfalfa as pasturage resultsin high gains per animal and per acre, owners fearedanimal losses due to bloat. Despite these disadvantages,alfalfa fits well in controlled grazing systems, providinga high-quality pasture with excellent drought toler-ance. Widespread availability of the antibloat supple-ment poloxalene, electric fencing, increased harvestcosts, and grazing management techniques capable ofmaintaining alfalfa stands have led to greater interest ingrazing alfalfa. Recent plant-breeding efforts suggestthat cultivars with low bloat potential and more persis-tence under grazing are possible and should furtherincrease the use of alfalfa in pastures.

Effective grazing management requires some knowl-edge of how animals graze and make use of forage.Under pasture conditions, animals tend to select, ofthe plants available, those of higher nutritional quality.Chemical analysis of forage samples indicates that theychoose mainly the soft leaves and stems as they graze.Voluntary intake of alfalfa is higher than that of otherpasture species. Alfalfa is a highly digestible, nutritiousforage whose dietary potential can be maximized byrotational grazing. Grazed alfalfa supplies all livestock

protein needs. Much of the protein will be degraded toammonia in the rumen and converted to amino acidsby rumen microbes, which are then absorbed in theanimal’s hindgut. Dietary energy supplementationmay help maximize gain. For example, high-producingdairy cows that graze alfalfa may benefit from rumen-degraded protein supplements.

In the Intermountain Region, options for grazingalfalfa include the following:

• dormant-season grazing of alfalfa stubble• grazing as a substitute for an early- or late-season

cutting• rotational grazing of alfalfa during the growing

season

This chapter will describe each of these options andoutline grazing management strategies to optimizeanimal production without sacrificing alfalfa vigorand stand life. It will also discuss the health problemsthat are most often associated with alfalfa pasturage.

127

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ALF

ALF

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D O R M A N T- S E A S O N G R A Z I N G

Of the three alternatives listed, dormant-season graz-ing of alfalfa is the most widely used in California atpresent. This option utilizes, as cattle or sheep feed,the forage produced between the final harvest and thefirst killing frost. Dormant-season grazing—that is,grazing during the early winter months—often mesh-es well with the lambing season.

Recent studies have shown that dormant-seasongrazing may be an effective integrated pest manage-ment (IPM) strategy because it reduces weed andinsect pests. In Oklahoma, cattle grazing during dor-mancy reduced the number of overwintering alfalfaweevil eggs by 60 percent and reduced the populationof the weevil parasite Bathyplectes curculionis by lessthan 12 percent. New Zealand researchers reportedthat, during dormant-season grazing, the number ofoverwintering blue alfalfa aphids decreased from 220to 2.5 per stem. Dormant-season grazing may reducerodent populations because it decreases winter cover.

In many areas of California, dormant-season graz-ing occurs during periods of wet weather. This raisesconcerns about soil compaction from trampling,increased crown damage or disease, and reduced standdensities. Studies at the University of California,Davis, and in the southern San Joaquin Valley revealedthat dormant-season grazing caused no change ineither soil bulk densities or alfalfa stand density. Otherresearchers reported that trampling caused few detri-mental effects. Animal holding areas apart from thealfalfa field can minimize damage, especially in areaswith heavy clay soils and in wet weather.

Several management tactics can optimize dormant-season grazing. Nevada guidelines recommend initiat-ing grazing soon after a killing frost, to maximize

forage quantity and quality before shattering and leach-ing losses occur. To avoid bloat, wait until leaves turnbrown. (Bloat is discussed later in this chapter.) In areaswhere snow cover occurs, leave a 3-inch stubble tocatch snow—this will decrease frost heaving andreduce cover for overwintering mice. In milder cli-mates, hold animals in the field until they completelyconsume the old stems. Getting rid of these willimprove the quality of the first cutting. Growers canexpect that grazing animals will remove about 0.5 tonforage per acre during the winter period. To preventyield loss, remove animals before spring growth begins.

G R A Z I N G A S A S U B S T I T U T E F O R C U T T I N G

This option is most often used in spring or fall, beforethe first or last cutting, when inclement weatherthreatens the ability to harvest a quality hay crop(Figure 14.1.). In general, spring grazing delays thenext harvest by the approximate length of the grazingperiod. Spring grazing does not affect the yield of sub-sequent cuttings. With sound management, substitut-ing grazing for harvesting has no detrimental impacton the alfalfa stand.

For early spring grazing, turn animals into the pas-ture when alfalfa is approximately 4 inches high. Userotational grazing to manage animal pressure so thataverage plant height does not exceed 5 to 7 inches(this will help maintain some leaf area). If the pasture


Figure 14.1. Grazing often substitutes for a fourth cutting whenweather conditions make it difficult to properly cure a hay crop.

Alfalfa is a highly digestible,nutritious forage

whose dietary potential can be maximized

by rotational grazing.

g r a z i n g m a n a g e m e n t 129

will be cut later, for hay, allow a recovery period of atleast 40 days before harvesting the crop.

If more than one grazing is substituted for cuttingduring the growing season, follow these guidelines:

• Make one or two cuttings between the grazingcycles.

• Allow regrowth to go into the bloom stage beforeanimals are permitted to graze.

• Maintain a short grazing period.

With the onset of cold, wet fall weather, grazingmay be an alternative to a fourth cutting. Grazing mayallow you to retrieve an additional 0.5 to 1.0 ton peracre of fall growth. Allow the alfalfa to reach bloomstage before grazing begins. This enables plants tostore adequate root carbohydrates prior to frost. Thisapproach is similar to that for dormant-season grazing.

ROTAT I O N A L G R A Z I N G D U R I N G T H E G ROW I N G S E A S O N

Rotational grazing of alfalfa during the growing seasonoffers much potential for high gain per animal and peracre. In humid regions, owners of beef steer and mar-ket lamb have realized liveweight gains of 1,000 and900 pounds per acre, respectively. Rotational grazing ispreferable to continuous grazing because it maintainsstand vigor and maximizes production.

Do not allow animals to graze before alfalfa reachesearly flowering stages. This ensures that root carbohy-drate reserves are not depleted, and it decreases thepotential for bloat. Grazing periods less than 2 weekslong prevent animals from grazing regrowth; sheepshould have a shorter rotation schedule than cattlebecause they graze more closely. Most experts suggesta period of 28 to 42 days for recovery following graz-ing, or approximately the length of the usual hay har-vest during the growing season. Divide the alfalfa fieldinto a number of paddocks (generally four to nine),and rotate the animals through the paddocks as theygraze the alfalfa. During periods of peak alfalfa pro-duction, some paddocks may be cut for hay instead ofbeing grazed. Also establish a separate loafing area forwatering and mineral supplementation.

Grazing management is the key to maximizing live-stock gains without detriment to the alfalfa stand.Advances in electric fencing have made labor and

management aspects of rotational grazing of alfalfaand other forage crops simpler and more cost-effective(Figure 14.2). Different classes of livestock mayrequire somewhat different rotational grazingschemes. To maintain a percentage of leaf in the dietthat will maximize gains, allow market lambs a shortergrazing period than other animals.

To maintain high quality, graze alfalfa closely toremove older, lignified stems. Recommended stubbleheights as animals leave the field range from 4 to 5inches to 6 to 8 inches, or when new crown shootsappear. This may be accomplished by using a leader-follower system, whereby animals on a high-nutritionregime rotate into a new paddock several days ahead of“cleanup” animals, whose nutritional needs can be metwith the lower-quality feed left behind. A leader-follower system might be used for stocker steers fol-lowed by dry mature cows, for example. Another alter-native is creep grazing, whereby young calves areallowed into new paddocks through fence gaps. Theyare then followed by their dams, who rotate into the“creep” paddock after they graze down the present one.

Stocking rates on alfalfa should be based on the fol-lowing factors:

• forage production (estimated from previous hayyields)

• nutrition needs and estimated intake of the class oflivestock

• percentage of forage utilized (Use 50-percent utilization as a rule of thumb.)

Figure 14.2. Advances in electric fencing have facilitated rotationalgrazing of alfalfa and other forages. Electric fences are a psychologi-cal barrier, not a physical barrier (like a barbed-wire fence). A fewcattle may not adapt to electric fences and have to be removedfrom the herd so that producers can effectively manage the remain-der of the cattle.

VE

RN

MA

RB

LE

Be conservative in your estimates and flexible inadjusting the stocking rate.

A G RO N O M I C P R A C T I C E S

Procedures for stand establishment (see chapter 2),irrigation (see chapter 4), and fertilization (see chapter5) of alfalfa for pasturage are the same as those foralfalfa hay or silage. Schedule irrigation for periodswhen animals are not grazing the paddock. Since ani-mals return some nutrients to the soil, via urine andfecal material, use soil or plant tissue tests to deter-mine the need for fertilizers (see chapter 5).

A N I M A L M A N A G E M E N TC O N C E R N S

Frothy Bloat

The potential for livestock death due to frothy bloathas been a major obstacle to widespread use of alfalfaas pasturage. Bloat results when ruminant animalsretain the gases produced during microbial fermenta-tion of forage in the rumen. A stable foam develops,and it prevents the escape of gases through eructation.The rumen swells into the abdominal cavity, where itinterferes with body processes and may cause death.Symptoms of bloat include frequent urination anddefecation, arched back, labored breathing, and lollingof the tongue. Economic ramifications includereduced weight gains and feed efficiency, lower milkproduction, and increased veterinary and labor costs.

Occurrence of bloat is linked to periods of lush,rapid growth of certain forages, including alfalfa.Typical suspect species are high-nitrogen, easily digest-ed forages with low dry-matter and fiber contents.Individual animals can be particularly susceptible tofrothy bloat. Once identified, chronic bloaters shouldbe permanently removed from the pasture.

Several management strategies can help decreasethe incidence of bloat caused by grazing alfalfa.Beginning 5 to 7 days before alfalfa grazing starts, giveanimals a daily dose of 1 to 2 grams poloxalene per100 pounds body weight. This antifoaming agent isavailable in block, liquid, or pellet form. If fed in

block form, it should be the only source of salt andminerals. To increase the likelihood of consumptionby all animals, place the poloxalene near loafing andwatering areas. Monensin and other ionophore sup-plements also appear to decrease bloat incidence.

Alfalfa is most likely to cause frothy bloat duringvegetative growth. Do not let animals graze until afterflowering begins. Prior to initial turnout, fill the ani-mals up on grassy or stemmy hay, and, if possible,leave all animals on the alfalfa pasture continuously.When rotating between pastures, move cattle in latemorning through the afternoon, after they havegrazed. Never move very hungry animals to new pas-tures. Regular supplementation with dry hay may benecessary.

A compatible grass—such as ryegrass, orchardgrass,or bromegrass—planted with alfalfa can decreasebloating. Animals tend to graze the grass first, whichmay decrease gains somewhat compared to those real-ized from a pure alfalfa pasture. Because the severity ofbloat increases when alfalfa is irrigated while animalsgraze, do not irrigate when animals are present. Cool,wet, cloudy weather may also increase chances ofbloat. By applying the management practices this sec-tion recommends, you can reduce losses due to bloatto less than 5 percent.

Plant breeders in Canada began trying to develop abloat-safe alfalfa in 1970. They recognized that rapidinitial digestion is a major contributor to bloat, sotheir efforts have included the attempt to produce analfalfa cultivar that is digested slowly. Researchers cau-tion that it may be some time before such a cultivar iscommercially available.


The potential for livestockdeath due to frothy bloat has

been a major obstacle to widespread use of alfalfa

as pasturage.

Estrogen Problems in Sheep

Sheep are especially susceptible to phytoestrogens,plant-produced compounds that mimic estrogen wheningested by ruminants. Alfalfa and certain Trifoliumspecies (notably subterranean clover) can induce infer-tility in sheep because these plants contain phytoestro-genic compounds. To avoid fertility problems, do notallow sheep to graze alfalfa for 2 weeks prior to breed-ing and until 2 weeks after conception.

Other Health Problems

Enterotoxemia, overeating, and clostridium C & D arethree causes of sudden death whose symptoms mimicthose of frothy bloat. Minimize the potential for thespread of disease by ensuring that all animals on alfalfapasture receive vaccinations for infectious diseases atintervals recommended by a veterinarian. Make ade-quate water and trace minerals (including salt) avail-able on a free-choice basis. Check animals once ortwice each day so that any appearing injured, bloated,or distressed can receive care promptly.


Certified Alfalfa Seed Council. 1988. Grazing alfalfa pamphlet.Davis, CA.

Cope, G. E., and F. C. Peter. 1976. Bloat control of animals grazingon alfalfa pasture. Texas Agricultural Experiment Station FactSheet Number l–1496.

Jensen, E. H., R. R. Skivington, and V. R. Bohman. 1981.Dormant season grazing of alfalfa. Reno: University of Nevada.Agricultural Experiment Station Report R142.

Krysl, L. J., S. R. Lewis, G. B. Wheeler, and R .C. Torell. 1989.Grazing alfalfa. Reno: University of Nevada CooperativeExtension Fact Sheet 89–22.

Roberts, B., C. Frate, and V. Marble. 1988. Grazing alfalfa withsheep: Does it affect yield or stand life? Proceedings, 18thCalifornia Alfalfa Symposium, 1–5. December 7–8, Modesto,CA.

Van Keuren, R. W., and G. C. Marten. 1972. Pasture productionand utilization. In C. H. Hanson (ed.), Alfalfa science and tech-nology, 641–58. Madison, WI: American Society of Agronomy.Number 15.

g r a z i n g m a n a g e m e n t 131

C H A P T E R F I F T E E N

M A N A G E M E N TA N D R E P L A C E M E N TO F D E P L E T E DS TA N D SSteve B. Orloff and Daniel H. Putnam

�he rate of decline of an existing stand canbe slowed by selecting an adapted varietywith persistence and by practicing good

management. Inevitably, however, the stand will thindue to diseases, winter injury, and other factors,including mismanagement. Yield, quality, and profitwill fall to a point where a decision regarding the fateof an older stand must be made.

This decision is greatly influenced by the profitabil-ity of available rotation crops. Unfortunately, theshort growing season and cool climate in theIntermountain Region limit rotation crop options.For most of the region, rotation crops (primarily cere-als) are less profitable than alfalfa. Furthermore, estab-lishing a new stand of alfalfa is expensive—cash costsfor establishing a stand are over $200 per acre. Thischapter will discuss methods to evaluate old stands,management options for thin stands, and techniquesfor removing old alfalfa stands.

E VA L U AT I N G O L D S TA N D S

Calculate Stand Density

Both forage yield and quality are directly related tostand density. Traditionally, alfalfa stands are evaluatedby using plant counts to determine the number ofplants per square foot (Table 15.1). Based on thismethod, stand densities below three to five plants persquare foot should be replaced (Figure 15.1) becausethese stands usually yield less than 4 tons per acre(actual yield varies depending on production area).Furthermore, forage quality declines as weeds invadeopen spaces between plants.

133

The problem with using plant counts to assessstands is that all crowns are counted equally. However,a small weakened plant is not nearly as productive as alarge healthy plant. Research in Wisconsin hasdemonstrated that the number of stems per squarefoot is a better reflection of productivity than is thenumber of plants. Results showed that fields with 55or more stems per square foot (measured at 6 inches ofregrowth) produced maximum yields and that fieldswith fewer than 40 stems per square foot were notprofitable and warranted replacement.

Analyze the Economics of Stand Removal

The matter of when to remove an alfalfa field is pri-marily an economic decision. The anticipated yield,quality, and price of alfalfa produced from a new fieldmust be compared with that of the existing stand.Remove a stand when its productivity has declined tosuch a degree that net profits would be greater if thealfalfa were removed and a new crop established.

Unfortunately, the economics of stand removal arenot simple; a grower must consider several factors inaddition to productivity and forage quality (Figure15.2). Rotation requirements, the income or loss thatoccurs with rotation crops, the amount of forageneeded, the strength of the alfalfa market, and theopportunity cost of money spent on stand establish-ment (that is, what else could you do with the money)all enter into the decision. Any of these factors canreverse a decision based on production alone. In addi-tion, pest pressures may dictate that an alfalfa stand bereplaced before its production level indicates it is nec-essary. Diseased fields may need to be removed earlydue to rapid stand decline or to prevent diseases (suchas verticillium wilt) from spreading to healthy fields.Severe infestations of unpalatable or perennial weedsmay require that an alfalfa field be plowed out.Similarly, stand removal may be the only economicalmeans of dealing with serious outbreaks of rodentpests.

U N D E R S TA N D I N G M A N A G E M E N T O P T I O N S

When faced with a depleted alfalfa stand, growershave two options: stand extension and stand replace-ment. The next two lists present the alternatives asso-ciated with each choice.

Stand extension• Continue to harvest a poor alfalfa stand. • Interseed another forage plant.• Overseed with alfalfa.

Stand replacement• Replant alfalfa after removing old stand (produce

back-to-back alfalfa). • Remove stand and rotate to another crop.

Factors to be considered when deciding whichoption to pursue include pressure from diseases, pests,and weeds; rotation requirements; total acreage andtype of forage desired; and the projected status of thealfalfa hay market. Prolonging stand life is unwise ifdisease pressure is severe. Likewise, if fields are heavilyinfested with rodents or difficult-to-control perennial


Table 15.1. Minimum stand densities for different production years.

E N D O F S TA N D D E N S I T Y P RO D U C T I O N Y E A R ( N O . O F P L A N T S / F T 2)

1 10–20

2 8–12

3 6–9

Any year 3–5—Replace stand

Figure 15.1. Alfalfa stands below five plants per square foot result inlost yield. (Data obtained from fifth-year stands in a 1985 variety trial,Tulelake, California.)

6.0

5.5

5.0

4.5

4.0

3.5

6.5

Plant stand (plants/sq. ft.)Yi

eld

(tons

/A)

2 3 4 5 6 7 108 9

m a n a g e m e n t a n d r e p l a c e m e n t o f d e p l e t e d s t a n d s 135

weeds, remove the stand. If you have insufficient for-age acreage, consider interseeding, overseeding, orreplanting alfalfa after alfalfa. High hay prices areanother incentive for extending stand life. However,continuing to harvest a poor alfalfa stand is not usual-ly a viable option. In general, intermountain alfalfastands remain in production for too many years ratherthan too few.

S TA N D E X T E N S I O N

Interseeding

The costs of interseeding poor stands with grasses arecomparable to those of herbicide application. Inter-seeding may preclude the need for an herbicide andalfalfa weevil treatment. Also, yields of mixed alfalfa-grass fields are frequently over 1 ton higher than thoseof older, pure-alfalfa stands. The economics of inter-seeding are market related and depend on the pricedifferential between pure alfalfa and an alfalfa-grassmixture. The market for mixed hay is primarily forhorses, but mixed hay is also fed to cattle and drycows. The price difference between pure alfalfa andalfalfa-grass mixtures depends on the visual appear-ance of the hay and the strength of the horse hay orstock hay market. Alfalfa-grass hay sometimes sells foras much as pure alfalfa hay in areas that have devel-oped a strong horse hay market.

Many alfalfa growers target the dairy market andstrive to produce top-quality “high-test” hay.However, with a large acreage, maintaining dairyquality on all fields is difficult because of the timerequired to swath, cure, and bale numerous fields. Tomaximize quality when growing several fields, cutyoung high-producing fields first and manage them toproduce hay of high nutritional quality. Interseedfields of older, thinner alfalfa stands to prolong standlife and maintain yields. Cut these fields last with thegoal of maximum yield in mind, and market the hayfor horse and other nondairy use.

Interseeding annualsIt is a common practice in some areas to interseed oatsor, less frequently, awnless (beardless) barley or wheatinto a thin stand of alfalfa. This usually improves firstcutting yield—a 4-ton yield is common. Herbicidesare not needed, and interseeding often reduces thealfalfa weevil population. To interseed, first cultivatewith a harrow or disc in late winter or early spring.This kills emerged weeds and prepares a suitableseedbed. The interseeded species is usually planted by drilling, but it could be broadcast and harrowed(Figure 15.3). The preferred seeding rate depends onthe alfalfa stand density (higher seeding rates for thin-ner stands), but 50 to 75 pounds of oat seed per acrehas produced maximum yields in most research trials.The amount of nitrogen fertilizer to apply variesdepending on soil type and fertility. Most tests haveindicated that 40 to 60 pounds of nitrogen per acre isadequate to supplement the nitrogen that is suppliedby the alfalfa crop. The forage produced is not suitablefor milking dairy cows, but it is widely accepted forother classes of livestock, particularly horses.Researchers continue to search for alternative annualsfor interseeding, such as beseem clover, which has for-age quality nearly equal to that of alfalfa.

• Estimated annual yield of old versus new stand • Production costs of old versus new stand• Comparison of quality, marketability, and price

of hay from old and new stands• Anticipated strength of hay market• New stand establishment expenses• Expected new stand life• Profitability of rotation crops• Rotation crop requirements• Quantity of forage desired• Pest problems (diseases, weeds, rodents)• Opportunity for other investments

Stand densities below three to five plants per square foot

should be replaced.

Figure 15.2. Factors to consider when deciding whether to replacean alfalfa stand.

The drawback of interseeding oats or other cerealsis that they are usually headed-out when harvestedand do not recover after cutting. Therefore, they donot contribute to increased yields in subsequent cut-tings. In fact, second cutting yields from fields inter-seeded with oats are often slightly lower than fields notinterseeded. This is most likely the result of damage tothe alfalfa during cultivation for interseeding and ofcompetition from the interseeded crop. The alfalfausually recovers, and yields of later cuttings are com-parable to those of pure alfalfa stands. Nonetheless,most growers harvest only one cutting when interseed-ing cereals into alfalfa. After one harvest, they removethe alfalfa and rotate to a different crop.

Interseeding perennialsPerennial grasses interseeded in alfalfa contribute for-age beyond the first cutting and may extend stand lifefor several years (Figure 15.4). Researchers have evalu-ated the suitability of several grass species for inter-seeding. These include perennial ryegrass, tall fescue,kemal festulolium (ryegrass x tall fescue), orchardgrass,timothy, and matua prairiegrass. Orchardgrass appearsto be the species best suited for interseeding. It is highyielding, very palatable, and compatible with alfalfa.Some dairies accept alfalfa-orchardgrass, and it is high-ly desired by many retail feed stores for pleasure-horsehay. Tall fescue is high yielding but extremely aggres-sive; over time, it chokes out alfalfa. Ryegrass is highyielding for the first cutting, but it also tends to be verycompetitive with alfalfa. Also, ryegrass has not persist-ed well in some parts of the Intermountain Region.Matua prairiegrass, like orchardgrass, is highly palat-able, but it is less competitive; unfortunately, yields offields interseeded with matua grass were lower thanthose with orchardgrass in initial tests. Alfalfa-timothyinterseedings are highly desirable because of theirpotential marketability to the horse industry, but todate alfalfa-timothy hay has not received a premiumhigher than that for other alfalfa-grass hays. Timothydoes not compete well, so stand establishment can beslow and difficult, particularly when interseeding.Nevada growers have had success killing alfalfa instrips by using glyphosate (Roundup) prior to inter-seeding timothy. Tests have shown that timothy doesnot yield well the first year after seeding, but it per-forms well in later years if planted on proper soil types(medium- to fine-textured soils).

Methods for interseeding perennial grasses are simi-lar to those for interseeding cereals. Fields are cultivat-ed with a harrow or disc in the late winter or earlyspring (this kills emerged weeds and prepares aseedbed). Fall seedings, after the last alfalfa cutting ofthe season, are possible, but weed infestations may besevere. Winter annual weeds emerge with the inter-seeded crop, and most available herbicides cannotcontrol them.

The interseeded perennial grass is usually drilledusing the small-seed attachment of a grain drill. No-till drills can be used for seeding, but tillage is usuallybeneficial to control emerged weeds. Seed can bebroadcast and incorporated with a ringroller or culti-


Figure 15.3. Use of a stand grain drill to interseed forage grassesinto a thin alfalfa stand.

Figure 15.4. Timothy interseeded into a depleted alfalfa stand.

packer; if you do so, increase seeding rates slightly.Seeding rates, per acre, depend on the seed size of theinterseeded species: 5 pounds timothy; 10 to 12pounds orchardgrass, ryegrass, or tall fescue; or 30pounds matua grass. Perennial grasses are slow tobecome established and should be interseeded beforethe alfalfa stand becomes too thin (this is especiallytrue for timothy). Perennial grasses can be interseededalong with a low rate of oats (50 pounds per acre orless) to improve yields in the first cutting after inter-seeding. This practice may slow the growth of theperennial grasses, however. Unlike pure-alfalfa stands,apply nitrogen to alfalfa-grass mixtures annually(approximately 50 to 75 pounds nitrogen per acre issufficient).

Overseeding with Alfalfa

It is tempting to thicken an old stand by overseedingwith alfalfa. Conceptually, overseeding should sub-stantially reduce the costs associated with establishinga new stand. Unfortunately, successful overseeding isdifficult at best. Seedling emergence following over-seeding is often adequate, but most seedlings fail tosurvive. As a result, only the original stand remains.

Several explanations account for overseeding fail-ures. First, diseases, and insect and nematode popula-tions frequently increase in established stands. Theolder plants can withstand them, but they destroy vul-nerable seedlings. The second reason involves competi-tion. Alfalfa seedlings grow slowly and are not verycompetitive. They have to compete for light, water,and nutrients with other alfalfa plants and weeds thatmay be hundreds of times their size. Competition forlight and water is usually the most severe. After surfacewater is depleted, seedlings may succumb to droughtstress, whereas deeper-rooted older plants thrive.Large, vigorously growing plants shade seedlings, fur-ther reducing top and root growth and water uptake.Third, germinating alfalfa seeds may be exposed toautotoxic compounds. Autotoxic compounds are nat-urally occurring chemicals that are released fromleaves, stems, and roots of older alfalfa plants (but areconcentrated in leaves). These compounds reduce ger-mination and retard seedling development. Lastly,after many years of producing a perennial crop underirrigation, the seedbed surface is not usually ideal.

Despite these obstacles, some growers claim successat thickening alfalfa fields by overseeding. These suc-cesses may be highly specific to site—especially to soiland weather conditions. At best, consider overseedinga risky practice. Growers who attempt overseedingshould pay particular attention to these factors:

• Weed and insect control: Many insects feed onyoung plants.

• Irrigation: Seedlings compete poorly for moisture,so you should irrigate frequently. Consider a 4-dayirrigation cycle to provide adequate moisture forgermination and establishment.

• Time of seeding: Seed when competition fromestablished plants is minimal—perhaps in early fallor between second and third cuttings.

• Seeding technique: Plant 1⁄4 to 3⁄8 inch deep.Planting too deep will increase the probability offailure.

S TA N D R E P L A C E M E N T

Stand Removal Practices

Alfalfa can be remarkably difficult to kill. Bothmechanical and chemical methods are employed toremove old stands. Mechanical techniques includeplowing, rototilling, multiple discings, and undercut-ting with wide sweeps. A rotary tiller is the most effec-tive implement for removing alfalfa, but it is expensiveand time-consuming to operate. Plowing is perhapsthe most common method of stand removal, butplowing is often undesirable in rocky or shallow soils.Several passes are normally required when ripping ordiscing an old stand.

Herbicides are useful to remove alfalfa on rocky orerodable soils. Roundup (glyphosate) is the most fre-

m a n a g e m e n t a n d r e p l a c e m e n t o f d e p l e t e d s t a n d s 137

Orchardgrass appears to be the species best suited

for interseeding.

quently used product for this purpose. However, highrates or retreatment may be needed because alfalfa iscomparatively tolerant to Roundup. Dicamba(Banvel) or 2,4-D (several products) can be used aloneor in combination with Roundup, provided no cropssensitive to growth regulator-type herbicides are neartreated fields. Herbicides may need to be combinedwith tillage for complete control. Regardless of themethod used, alfalfa crowns must be desiccated (com-pletely dried) to reduce the possibility of regrowing.

Back-to-Back Alfalfa

In areas where rotation crops are more profitable thanalfalfa, these rotation crops often dictate when andhow often fields are planted to alfalfa. However, asstated earlier, few profitable rotation crops exist formuch of the Intermountain Region. Growers who donot have alternative crop options or who are experi-encing extreme market forces or on-farm needs gener-ally plant alfalfa directly after alfalfa.

Planting alfalfa back to back is fraught with many ofthe problems associated with overseeding alfalfa into anexisting stand. Even if chemicals or tillage creates a non-competitive environment for young seedlings, theseedlings must still contend with autotoxic compounds,diseases, and pests. The effect of autotoxic compoundsprobably dissipates within 2 to 3 weeks following standremoval, but diseases and pests persist much longer.Rotation to another crop for one year usually allowsenough time for diseases and pests to dissipate.

Crop Rotation

The many benefits of crop rotation are well estab-lished, and most agronomists recommend crop rota-tion, rather than continuous cropping, for almost allspecies. Alfalfa is highly valued for its contribution toother crop species in a rotation. Benefits derived bysubsequent crops include nitrogen (which is biologi-cally fixed by the bacteria associated with alfalfa),greater water infiltration, and improved tilth. In turn,crop rotation benefits alfalfa. Rotation can break dis-ease and insect cycles and improve weed control andsoil fertility.


Chamblee, D. S., and M. Collins. 1988. Relationships with otherspecies in a mixture. In A. A. Hanson, D. K. Barnes, and R. R.Hill, Jr. (eds.). Alfalfa and alfalfa improvement, 439–61.Madison, WI: American Society of Agronomy, Crop ScienceSociety of America, and Soil Science Society of America.Number 29.

Orloff, S. B. 1993. Grass interseeding into established alfalfa.Proceedings, 12th Annual Nevada Regional AlfalfaSymposium, 93–8. February 17–18. Sparks, NV.

Undersander, D., C. Grau, D. Coscrove, J. Doll, and N. Martin.1994. Alfalfa stand assessment: Is this stand good enough to keep?Madison, WI: Cooperative Extension Publications, Universityof Wisconsin–Extension. Publication A3620.


k e y t o p l a n t s y m p t o m s 95

K E Y TO P L A N T S Y M P TO M S

How to use this key: Find the symptom in the left column, below. Read across to find the identifyingcode(s) of the possible problem(s). Use the codes toidentify probable causes in the column at right.

SYMPTOMS

Leaves ProblemSkeletonized I1, I5Chewed I4, I5, I6, I7 Curled and sticky I2, I3Yellow (veinal) H7Yellow between veins (interveinal) E4, H6, H8General yellowing of plant F1, F4, F6, D10 V-shaped yellow or dead tip D12 Small brown/black spots D9Yellow to pale green underside D8Tan marginal lesions D5 White marginal spots F3Red underside F5 Dark bluish/green E1, E3, F2, D2 Crinkled H9, I8 Narrowed (strapped) H3Clasped, or stuck together H1Burned (necrotic) E1, E2, E3, H4, H5 Darkened, water-soaked E2 Flagging and white D1

Roots Taproot rotted D3, D4 Tan or black root lesions D6 Vascular tissue red D11, D12Vascular tissue yellow/tan D4, D10 Chewed V1, V4 Cavities along sides I6 Galls on lateral roots D2 Stubby roots H2

Crowns Bluish/black dry rot D7Orange/red flecks D5Brown/yellow lesions D6

Shoots Stem and leaves eaten I7, V2, V3, V4, V5Wilting/flagging D4, D7, D12 Stunted and yellow D10Dead stem buds, swollen internodes D1Shortened internodes F5, D1, D12 Plant wilt, green stem D12

PROBABLE CAUSES

Problem Color Photo

ENVIRONMENTAL FACTORS E1 Salt E2 Frost 3.1 E3 Moisture stress E4 Abiotic/nonpathogenic

FERTILITY F1 Nitrogen 5.3 F2 Phosphorus 5.1 F3 Potassium 5.6 F4 Sulfur 5.4 F5 Boron 5.7 F6 Molybdenum 5.5

HERBICIDE INJURY H1 Eptam 6.1 H2 Balan H3 2,4-DB 6.2 H4 Buctril 6.3 H5 Gramoxone H6 Velpar 6.4 H7 Karmex H8 Sencor H9 Roundup 6.5

INSECTS I1 Alfalfa weevil 7.1–7.3 I2 Pea aphid 7.4 I3 Blue alfalfa aphid 7.4 I4 Alfalfa caterpillar I5 Armyworm I6 Clover root curculio 7.5 I7 Grasshoppers I8 Thrips 7.6

DISEASES AND NEMATODESD1 Stem nematode 8.1–8.3 D2 Root-knot nematode 8.4 D3 Pythium 9.1 D4 Phytophthora root rot 9.2 D5 Stagonospora crown/root rot D6 Rhizoctonia root canker D7 Anthracnose 9.3 D8 Downy mildew 9.4 D9 Common leaf spot D10 Bacterial wilt 9.5 D11 Fusarium wilt 9.6 D12 Verticillium wilt 9.7–9.9

VERTEBRATES V1 Gophers 10.1 V2 Squirrels 10.3 V3 Rabbits V4 Meadow mice 10.4 V5 Deer

Adapted by Steve B. Orloff from Canevari, W. M. 1993. Diagnosing field problems.Proceedings, 23rd California Alfalfa Symposium, 124–27. December 8–9, Visalia, CA.


3.1. Frost can be a problem almost anytime during the growing season,but it is most common in early spring. (A) Within hours after a hardfrost, leaves darken and appear water-soaked; stems may bend over.

5.1. Phosphorus deficiency, although characterized by stunted plantswith small leaves, is difficult—if not impossible—to identify visually,because many other problems cause similar symptoms. Contrast thephosphorus-deficient plants (left) with those that received phosphorusfertilizer (right).

5.2. Nitrogen, sulfur, and molybdenum deficiencies allcause yellowing and stunting. (A, B, C) These photos illustrate the progressive development of the deficiencyand chlorotic leaf symptoms (left) versus healthy leaves(right).

5.3. Nitrogen deficiency is evident soon after planting, when seedlingsreach 4 to 8 inches in height. In a field with nitrogen-deficient alfalfa,stunted yellow plants are scattered among taller dark green plants. Theyellow plants result from poor inoculation by Rhizobia bacteria; the darkgreen plants have been adequately inoculated.

(B) After a day, leaves—or parts of leaves—may become yellow orwhite. Typically, affected leaves fall from the stem a few days later.Severe frost may kill entire shoots.

A

A

B

B

C

CHAPTER 3

CHAPTER 5

JAC

K C

LA

RK

(3.

1A,

5.2

A,

B,

C),

ST

EV

E O

RL

OF

F (

3.1B

), R

OL

AN

D M

EY

ER

(5.

1, 5

.3)


B

C

D

5.4. Sulfur deficiency can occur at any time or growth stage, but it ismost common in spring, when alfalfa starts growing and soils are coldor wet. Contrast the yellow sulfur-deficient plants with the green nor-mal growth where sulfur was applied.

5.5. Molybdenum deficiency generally occurs after the first or perhapssecond cutting. Regrowth of molybdenum-deficient alfalfa, like that ofalfalfa deficient in sulfur, may be extremely yellow and stunted. Thisphoto shows a strip of yellow plants between green plants; the greenplants received an application of molybdenum.

A

5.6. (A) The upper portion of this alfalfa stemexhibits potassium-deficiency symptoms. (B)The first symptoms to appear are yellow orwhite spots, each about the size of a pinhead,near the margins of upper leaves. (C and D)As the plant becomes more deficient, leaf tipsand margins become more chlorotic. Whenleaves mature, the yellow tissue dies and turnsbrown.

RO

LA

ND

ME

YE

R (

5.4,

5.5

), J

AC

K C

LA

RK

(5.

6A,

B,

C,

D)


5.7. (A) The yellow andreddish chlorotic leaf tipsand margins associated withboron deficiency are some-what similar to potassium-deficiency symptoms. (B) Leaves of boron-defi-cient alfalfa are reddish pur-ple on the underside, andsometimes on the top. (C) After an irrigation, orwhen regrowth occurs, anew stem may initiate at thebase of the third or fourthleaf from the top of theplant. The new stem ap-pears normal at first, butthe internodes (stem seg-ments between leaves) be-come increasingly shorter.Later, the leaves of the newstem also exhibit boron-deficiency symptoms—yellow on top and reddishpurple on the underside.

6.1. The preplant herbicide Eptam may stunt seedlings and causecupped and clasped leaves, especially when it is applied to sandy soils.

6.2. Narrowed (strapped)leaflets can be a sign of injury bythe herbicide 2,4-DB. Suchleaves often become evidentwhen rain or sprinkler irrigationoccurs too soon after herbicideapplication.

6.3. Buctril can cause necrotic le-sions (dead spots) on plants, espe-cially if applied when weather isabove 80°°F.

6.4. Herbicides that are photosynthetic-inhibitors (Velpar, Karmex,and Sencor) can cause chlorosis, or yellowing, when applied after alfal-fa resumes growth in spring. (This photo shows Velpar injury.)

6.5. Actively growing alfalfa plants treated with Roundup becomestunted and have small crinkled leaves.

A

B C

CHAPTER 6

JAC

K C

LA

RK

(5.

7A,

B,

C),

BIL

L F

ISC

HE

R (

6.1,

6.4

, 6.

5) S

TE

VE

OR

LO

FF

(6.

2),

CH

AR

LE

S H

ICK

S (6

.3)


7.1. (A) First- and second-instar larvae of the alfalfa weevil feed on the tightly folded young leaves at the end of shoots. (B) Larger larvae feed on older leaves, giving them a (C) skeletonized appearance.

7.2. Once alfalfa weevil larvae complete theirgrowth, they spin silken cocoons on leaves orin debris on the soil surface.

7.3. The adult alfalfa weevil isdark gray to brown, with a darkbrown stripe on its back, andhas the distinctive weevil snout.The weevil can be seen for ashort time before it enters a rest-ing stage, which it spends inweedy areas near the field or infield trash.

A B

A

B

C

7.4. Both blue alfalfa aphids and pea aphids infest intermountain alfalfafields. (A) Blue alfalfa aphid causes significantly more stunting, but (B) pea aphid is more common in the Intermountain Region. The twoaphids can be distinguished by examining their antennae through a handlens. Blue alfalfa aphid antennae are uniformly dark; those of the peaaphid have dark bands on light green antennae. The pea aphid on theright has been parasitized by a wasp of the genus Aphidius.

A

B

7.5 (A) White larvalforms of the cloverroot curculio (8Xmagnification)begin feeding on fibrous roots. (B) They subse-quently chew largecavities along thesides of taproots.

7.6. Feeding by thrips causes wrinkled and distorted leaves.

CHAPTER 7

JAC

K C

LA

RK

(7.

1A,

B,

C,

7.2,

7.3

, 7.

4A,

B,

7.5A

), L

AR

RY

GO

DF

RE

Y (

7.B

), S

TE

VE

OR

LO

FF

(7.

6)


8.3. Stem-nematode infestation typically occursin patches of the field in spring, when weather iscool and wet.

A B

8.1 Stem nematode-infested plants have dead stem buds and short,swollen internodes. The shoots on the right are normal.

8.2 Shoots that are slightly smaller than normal and completely whiteare symptomatic of a stem-nematode infestation. Such shoots are mostprominent after the first cutting.

8.4. (A) Root-knot nematode causes galls onlateral roots. (B) Unlike galls, nitrogen-fixingnodules are pinkish and easily dislodged byrubbing.

9.1. The seedling on theleft is healthy; the otherthree show differentsymptoms of seedlingdisease. The secondseedling has a brown lesion and an abnormal-ly thick root below it. The root of the thirdseedling has thepinched-off look typicalof plants infected byPythium fungi. Bygrowing new roots, theseedling on the right hasrecovered from an earli-er infection.

9.2. (A) Phytophthora root rot lesions are yellow-brown to blackand eventually girdle the taproot. The taproot usually rots wherewater drainage is impeded. (B) When a phytophthora-infected rootis sliced vertically, red-orange to yellow streaks, which spread upseveral inches from the rotten root tip, become visible.

CHAPTER 8

CHAPTER 9

STE

VE

OR

LO

FF

(8.

1, 8

.3),

VE

RN

MA

RB

LE

(8.

2, 9

.2A

, B

), J

AC

K C

LA

RK

(8.

4A,

B,

9.1)


B

9.3. (A) Symptoms of anthracnose includedead straw-colored stems that are bent andsometimes scattered through fields. (B)Straw-colored oval or diamond-shaped lesionswith a brown border are found on stems of in-fected plants. (C) When diseased stems are re-moved from the crown, a blue-black crownrot is visible.

9.4. (A) Light green to yellow patches onleaflets are characteristic of downy mildew (a foliar disease common to intermountainalfalfa). (B) On the underside of leaves infect-ed with downy mildew is a fine grayishgrowth of spore-bearing structures.

A B

A

C

9.5. The small, yellowish plant in the fore-ground has bacterial wilt. Severely infectedplants are stunted and have spindly stems andsmall, distorted leaflets.

9.6. A longitudinal cross section of afusarium wilt-infected root reveals adark reddish brown discoloration inthe stele, or center, of the root.

9.7. Foliar symptoms of verticillium wilt are similar tothose caused by gopher feeding. However, the stems ofplants infected with the disease do not wilt and usuallyretain their green color. Near the top of shoots, thestems between the leaves (internodes) are short, andthe plant cannot be pulled out of the ground easily.

JAC

K C

LA

RK

(9.

3A,

B,

9.4B

), S

TE

VE

OR

LO

FF

(9.

4A),

VE

RN

MA

RB

LE

(9.

3C,

9.5)

, D

ON

AL

D B

AR

NE

S (9

.6),

RIC

HA

RD

PE

AD

EN

(9.

7)

A

A


10.1. Pocket gophers are rarely seen above ground, as in this photo;you may know they are present only by seeing the damage theycause—crescent-shaped mounds and scattered dead plants.

9.8. V-shaped yellowing, or chlorosis, of leaflets is a diagnostic symp-tom of verticillium wilt.

9.9. Rolled leaflets are characteristic of verticillium wilt.

10.2. (A) A tractor-drawnmechanical bait applicatoris useful for large areas. (B) It constructs an artifi-cial burrow and depositspoison grain at preset intervals.

10.3. (A) The California ground squirrelhas a flecked coat and long bushy tail. It isfound along field edges and fence lines. (B) In contrast, the Belding ground squir-rel is solid brown with a short, flat tail. Itinhabits alfalfa fields.

10.4. A series of trails (about 2 in. wide) thatlead to numerous short, moundless entranceholes indicates an infestation by meadowmice.

B

B

CHAPTER 10

RIC

HA

RD

PE

AD

EN

(9.

8, 9

.9)

JAC

K C

LA

RK

(10

.1,

10.2

B),

W.

PAU

L G

OR

EN

ZE

L (

10.2

A,

10.3

A),

ST

EV

E O

RL

OF

F (

10.3

B,

10.4

)

Date post:	18-Dec-2021
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INTERMOUNTAIN ALFALFA MANAGEMENT

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