Alfalfa Management Guide—Production (2 of 3)

Once a good stand has been

established, continued produc-

tion and stand life depends on

good management practices.

Good management includes

maintaining soil nutrients,

applying manure judiciously, and

controlling weeds and insects.

Monitor diseases to estimate

stand life and to determine

resistance needed in future

plantings. Finally, optimum

production involves deciding

when to rotate from stands that

are no longer profitable.

Production

Published byASA, CSSA, and SSSA

All copyrights reserved 2004

Fertilize annuallyDetermine needsAlfalfa has a relatively high demandfor some nutrients compared to othercommonly grown crops. Each ton ofalfalfa dry matter harvested removesabout 14 pounds of phosphate (P2O5)and 58 pounds of potash (K2O). Thisis the nutrient equivalent of 150pounds of a 0-10-40 fertilizer. Each tonof alfalfa also removes the calciumand magnesium found in about 100pounds of aglime. See table 4 for acomplete list of nutrients removed.Since many of these nutrients aresupplied from the native soil reserves,basing a fertility program onremovals is not recommended.

Soil tests are the most reliable methodfor preventing nutrient deficiencies.Visual symptoms (table 6 andpictures) can be used to help assessnutrient needs for future yield.However, by the time visual symp-toms appear on a crop, nutrient defi-ciency may be so severe that signifi-cant yield losses have alreadyoccurred. Visual symptoms can alsoreflect environmental conditions,restricted root growth, diseases orother problems not related to a soilnutrient shortage.Plant tissue analysis can determinethe nutritional status of your cropbefore any visual symptoms appear.While this method does not measurenutrient amounts for making a fertil-izer recommendation, combiningtissue analysis with a soil test makesfor a comprehensive nutrient manage-ment system.

18 ________________________________________________________________________ A L F A L F A M A N A G E M E N T G U I D E

Advanced techniquesTissue testing

Tissue testing is very useful for

assessing levels of sulfur and

micronutrients. It can detect nutrient

problems not easily detected with a

standard soil test. Sample the top 6

inches of mature forage in areas of the

field that are free of other problems

(insect, disease, drought, shade, etc.).

Follow specific sampling and data inter-

pretation guidelines to avoid misinter-

pretation. See table 5 for a list of

suggested sufficiency levels for the

essential nutrients.

Table 4. Pounds of nutrient removed perton of alfalfa produced, dry matter basis.

dry matter removed nutrient (lb/ton)

phosphorus (P) 6

phosphate (P2O5) 14

potassium (K) 48

potash (K2O) 58

calcium (Ca) 30

magnesium (Mg) 6

sulfur (S) 6

boron (B) 0.08

manganese (Mn) 0.12

iron (Fe) 0.33

zinc (Zn) 0.05

copper (Cu) 0.01

molybdenum (Mo) 0.002

Table 5. Sufficiency levels of nutrients, top 6 inches of alfalfa at first flower

nutrient low sufficient high

————————— % —————————

nitrogen <2.50 2.50–4.00 >4.00

phosphorus <0.25 0.25–0.45 >0.45

potassium <2.25 2.25–3.40 >3.40

calcium <0.70 0.70–2.50 >2.50

magnesium <0.25 0.25–0.70 >0.70

sulfur <0.25 0.25–0.50 >0.50

————————— ppm —————————

boron <25 25–60 >60

manganese <20 20–100 >100

iron <30 30–250 >250

zinc <20 20–60 >60

copper <3 3–30 >30

molybdenum <1 1–5 >5



19_______________________________________________________________________________________________________________________________________________________ P R O D U C T I O N ________________

Phosphorus deficiency

Deficient plants have yellowed leaves onshortened stems.

Leaflets often fold together, and theundersides may be red or purplish (left).

Deficient plants have blue-green leavesand stunted growth.

Potassium deficiency

Lower leaves of deficient plants areedged with white spots (left).

Leaves of severely deficient plants turncompletely yellow.

Sulfur deficiency

Leaves turn light green (left). Symptomsare similar to nitrogen deficiency.

Stems are spindly with weak growth.

Boron deficiency

Yellow coloring turns reddish to purplishbetween veins.

Table 6. Nutrient deficiency symptomsfor alfalfa.

nutrient deficiency symptoms

nitrogen Light green to yellow color,spindly growth.

phosphorus Blue-green color, stiff,stunted and erect growth.Leaflets often fold together,and the undersides andstems may be red orpurplish.

potassium White spots around edge ofleaf starting with lowerleaves. In advanced casesleaves turn completelyyellow and die.

calcium Impaired root growth orrotting. Petioles collapse onyoungest mature leaves.

magnesium Interveinal chlorosis of lowerleaves, margins initiallyremain green.

sulfur Light green, similar to nitrogen deficiency, spindlystems and weak growth.

boron Yellowing of leaves, short-ened main stem growthbetween upper portion ofshoots, dense top. Oftenconfused with leafhopperdamage.

manganese Interveinal chlorosis ofyounger leaves.

iron Interveinal chlorosis ofyoungest leaves, bleachedappearance.

zinc Reduced leaf size andupward curling of youngestleaves.

copper Severe curvature of petioles, grayish spots inmidleaf.

molybdenum Pale green and stunted aswith nitrogen deficiency.



20

NitrogenAlfalfa typically gets enough nitrogenfrom its symbiotic relationship withnitrogen-fixing Rhizobium bacteriaand from soil organic matter, whichreleases nitrogen as it decomposes.On well-inoculated, establishedstands, topdressed nitrogen does notimprove yields, quality, or standvigor. Normally, adding nitrogen maylower yield and/or quality by stimu-lating growth of grasses and weeds.But in some cases, such as where soilshave not been adequately limed, anapplication of 30 to 50 lb/acre ofnitrogen can be used as a stop-gapmeasure to increase yields.

Phosphate and potashAlfalfa needs relatively large amountsof phosphate and potash. Adequatephosphorus is important for success-ful establishment and good rootdevelopment. Potash is essential formaintaining yields, reducing suscepti-bility to certain diseases, and increas-ing winterhardiness and standsurvival. In the eastern portion of theMidwest, potassium is likely the mostlimiting nutrient to alfalfa production.Phosphate and potash are relativelyimmobile when added to the soil.Phosphate bonds tightly on acidicclayey soils (pH < 5.5) and on veryhigh pH soils (pH > 7.5) making itunavailable to plants. Potash canleach on some extremely sandy soilsand on organic soils (peat or muck).Applications of phosphate and potashshould be based on recommendationsfrom a recent, well-calibrated soil test.Since alfalfa may take up more potas-sium than the plant needs, whichcreates animal health problems, donot topdress potash on soils testingvery high for this nutrient. Foragetissue potassium levels should be

monitored if luxury consumption ofpotassium is suspected.Alfalfa absorbs most nutrients,including phosphate and potash, fromthe top 6 to 8 inches of soil. However,because phosphorus is immobile,alfalfa responds better to incorporatedapplications than to topdressed appli-cations. Guidelines for annual phos-phate and potash application includethe following:

1. Apply topdress nutrients immedi-ately after harvest and beforeregrowth resumes. Avoid contactwith wet foliage.

2. Topdress following first cutting tostimulate second and third cuttingregrowth or in early September toincrease winterhardiness.

3. Avoid application when soils aresoft (such as early spring) whenphysical damage to the alfalfacrown is likely.

4. Split the application to avoid saltdamage if more than 500 lb/acreof material (irrespective of grade)is to be used in any year.

5. Base fertilizer purchases on costper unit of plant food providedand need for all nutrientscontained in fertilizer. For example,since there is no difference in nutri-ent availability with red versuswhite potash or with ortho- versuspolyphosphate on most soils, thebest choice is the least expensiveproduct. Potassium-magnesiumsulfate may be a superior potas-sium source where sulfur isneeded and not supplied fromanother fertilizer material.

6. Foliar application should not beused for applying moderate tohigh rates of macronutrients,although it is an excellent methodfor applying micronutrients.

________________________________________________________________________ A L F A L F A M A N A G E M E N T G U I D E

Advanced techniquesManaging high potassium testing field

E xcessive forage potassium levels

in alfalfa (above 3%) can cause

milk fever and other anion balance

problems, especially for early-lactation

cows. Where producers are

concerned about forage potassium

levels, the following management tips

may help.

1. Use well-calibrated soil tests to

guide potassium applications. The

most severe forage potassium

excesses were observed when high

rates of potash were topdressed on

soils that already tested excessively

high for potassium.

2. Allow the alfalfa to mature a few

days longer. As alfalfa matures,

tissue calcium levels decrease.

3. Cut alfalfa as low as possible

without damaging the crown and

preserve leaves during harvest.

Potassium is concentrated in the

upper stems; therefore, including a

higher percentage of lower stems

and leaf tissue will lower forage

potassium levels by dilution.

4. All forages contain about the same

amount of potassium when grown

under similar environmental condi-

tions, so adding grasses or other

forages will not lower potassium

content.



Secondary nutrientsCalcium and magnesium deficienciesare very rare, especially where soil pHhas been maintained in the desiredrange for alfalfa. Symptoms ofmagnesium deficiency appear whenthe soil test drops below 50 to 100ppm magnesium. Magnesium candrop below that level on acidic, sandysoils where repeated high amounts ofpotassium have been applied; on soilswhere only calcitic liming materialshave been used; and on calcareousorganic soils. The most economicalway to avoid calcium or magnesiumproblems is to follow a good limingprogram with dolomitic limestone.Where soil pH is adequate and extramagnesium is needed, apply magne-sium sulfate (epsom salts) or potas-sium-magnesium sulfate (Sul-Po-Magor K-Mag) at 20 to 50 lb/acre magne-sium per year.Sulfur deficiencies are likely whenhigh sulfur-demanding crops such asalfalfa are grown on sandy soils or onother soils low in organic matter farfrom urbanized areas and which havenot received manure within the last 2years. Use of coal, fuel oil, and otherfossil fuels in industrial areas releasessulfur into the atmosphere that isdeposited on the land in precipitation.In general, precipitation containsenough sulfur to take care of cropneeds in most regions (10 to 25 lb/acreeach year). The amount of sulfur inmanure depends on the kind of

animal manure (table 7). Somesubsoils, especially those that areacidic and clayey, may contain enoughsulfur for high-yielding crops eventhough the plow layer may test low. Where the sulfur need has been estab-lished, either elemental sulfur or sulfateforms can be used on alfalfa. Sulfate-sulfur is immediately available to thecrop, whereas elemental sulfur must bebiochemically converted to sulfatebefore it can be used. When applied at25 to 50 lb/acre, sulfate-sulfur willgenerally be adequate for 1 or 2 years ofalfalfa production. In contrast, elementalsulfur applied at the same rate shouldlast for the term of the stand. Elementalsulfur converts to sulfate more rapidlywhen incorporated.

MicronutrientsPlants need only very small amountsof micronutrients for maximumgrowth. While a deficiency of anyessential element will reduce plantgrowth, overapplication of micronu-trients can produce a harmful level ofthese nutrients in the soil that is diffi-cult to correct, especially on coarse-textured soils. Soil tests are availablefor some micronutrients, but plantanalysis is generally more reliable foridentifying micronutrient problems.

Boron is usually the only micronutri-ent that is needed in a fertilizerprogram for alfalfa. Boron manage-ment depends on the texture of thesoil. Sandy soils do not hold boron astightly as clayey soils. A high test in asandy soil may be only medium in asilt loam. For alfalfa where the soil testis very low or low on medium-textured soils, apply 2 to 3 lb/acreboron once in the rotation. On sandysoils apply 0.5 to 1 lb/acre boron eachyear. Due to the low rate of materialneeded, boron is often mixed withother fertilizers such as potash. Do notapply boron near germinating seeds.Alfalfa has a relatively high require-ment for molybdenum. However,since molybdenum availabilityincreases as pH increases, liming tooptimal pH levels usually eliminatesmolybdenum problems. Manganese,zinc, iron, and copper are rarely defi-cient in alfalfa. In special situationswhere deficiencies are suspected,contact your county Extension officeor consultant before treating.

21_______________________________________________________________________________________________________________________________________________________ P R O D U C T I O N ________________

Table 7. Estimate of available sulfur from manure as affected by animal andmanure type.

————————— sulfur content —————————solid (lb/ton) liquid (lb/1000 gal)

kind of animal total available total available

dairy 1.5 0.8 4.2 2.3beef 1.7 0.9 4.8 2.6swine 2.7 1.5 7.6 4.2poultry 3.2 1.8 9.0 5.0



Irrigation Improper irrigation limits alfalfa yieldmore often than any other manage-ment factor in semi-arid areas. Wateruse is generally estimated as evapo-transpiration (ET), the combinedevaporated water from soil and plantsurfaces. In alfalfa, ET normally variesfrom 0.1 to 0.35 inches per day (figure16) producing a seasonal water use of36 inches per year in the semi-aridPacific Northwest and up to 72 inchesin the Southwest. Alfalfa yield is directly related to ET.Efficiency of water use is highestwhen the water supplied to plantsapproximates ET. In the Pacific North-west it takes about 5 inches of waterper acre to produce each ton of alfalfa.At 85% efficiency (15% of the waterevaporates before reaching soil), theactual application would need to beabout 6 inches.

Water for growth can come fromstored soil water, irrigation and rain.In heavier soils, water in the soilprofile from the previous fall’s irriga-tion and winter and spring precipita-tion will reduce irrigation waterneeded during the season. Stored soilwater may be crucial to high yieldsbecause of low water infiltration ratesin heavy soils. Sandy soils have muchless water-holding capacity but havehigher water infiltration rates.Plant stress can occur when availablesoil moisture falls below 50%. Thislost yield can not be “made up” byirrigating more than necessary follow-ing the stress! Border, corrugation (furrow),controlled flooding, and sprinkler irri-gation can be used on alfalfa. Choosethe method best suited to your slope,soil, water supply, and labor supply.

Irrigation scheduling is best accom-plished by the water balance method,in which calculations of water inputsequal outputs, can be used to estimatethe soil moisture condition. Use esti-mated water consumption providedby services such as AgriMet for irriga-tion scheduling where possible(www.usbr.gov). Use a soil probe orshovel to check soil moisture andverify the actual field conditions. Theroot zone should be filled with mois-ture just before the period of peakcrop water use.

Irrigation scheduling principles:

1. Begin season with full soil waterprofile.

2. Monitor the soil profile weekly formoisture content.

3. Soil water should be depleted toabout 50% of the available waterin the top 2 feet before harvest.The interval between irrigationand harvest varies from 2 days inlighter textured sandy soil at highsummer ET rate, to 13 days inheavier clay soils at low ET rates.The soil water reserve can be usedfor alfalfa growth when irrigationis halted for harvest or when theapplication rate can not keep upwith ET.

4. Begin irrigating again as soon asharvest is removed to refill the soilprofile. Stress during earlyregrowth will severely limit thenext crop yield.


Figure 16. Average evapotranspiration (ET) for alfalfa cut four times. Plants wereirrigated at maximum pivot capacity (6.5 gallons/minute, 85% efficiency). Note thatin midsummer the amount of water applied is less than the amount lost by ET. Thismeans the alfalfa must use soil moisture reserves or suffer reduced yield.

.40

.35

.25

.30

.20

.15

.10

.05

0

eva

po

rtra

nsp

ira

tio

n (

inch

es/d

ay) Max. pivot capacity

harvest: 4th3rd2nd1st

4/1 6/305/1 5/31 7/30 8/29 9/28 10/28

date



Manure management

Manure is a complete nutrientsource, containing all of the major

nutrients, secondary nutrients, andmicronutrients. In addition, manurepromotes biological activity in the soiland enhances the soil physical proper-ties. While manure may be beneficialto soil, applying manure on alfalfafields can create problems. Manurecan burn leaves, reducing yield andquality. The mechanics of applyingmanure can compact soil and damagecrowns which in turn lowers yieldsand shortens stand life. Also, nitrogenin manure can stimulate weed andgrass growth.If possible, spread manure on othercrops that can benefit from the nitro-gen. Alfalfa will use applied nitrogenbut does not need it due to its ability tofix nitrogen. When too much manureand/or too little cropland force appli-cation of manure to alfalfa, topmanagement practices are required. When alfalfa fields are the only landavailable for spreading manure, usethe following guidelines to reducedamage to the alfalfa stand:

1. Choose fields that have the mostgrass, usually the oldest stands,since these will benefit most fromnitrogen in manure.

2. Apply no more than 3,000 gallonsof liquid manure or 10 tons ofsolid manure per acre. Applyingmore may cause salt burn, anddamage or suffocate plants. Usesupplemental fertilizer if addi-tional nutrients are required.

3. Spread manure immediately afterremoving a cutting so manurecontacts the soil instead of thefoliage. This reduces the risk ofsalt burn and minimizes palatabil-ity problems.

4. Adjust the spreader to break uplarge chunks of manure that cansmother regrowth.

5. Spread manure only when soilsare firm to limit soil compactionand to avoid damaging crowns.

Weed management

Weeds reduce alfalfa productionduring establishment by compet-

ing with and choking out youngalfalfa seedlings. Weeds also invadeestablished alfalfa fields and reduceforage quality and alfalfa yield. Effec-tive weed control begins beforeseeding and continues throughout thelife of the stand. The most importantfactor in weed management is toestablish and maintain a vigorousalfalfa crop. Proper soil fertility andpH, seedbed preparation, varietalselection, and appropriate cuttingschedules cannot be over-emphasizedto prevent weed encroachment. Ifusing a herbicide, remember thatapplication timing and rates vary.Always read the product label forapplication instructions.

Weed management before plantingMost alfalfa stands are left in produc-tion for several years. The absence oftillage during the life of the standnaturally favors invasion by perennialweeds. It is very important to elimi-nate perennials before establishingalfalfa. Herbicides for perennial weedcontrol may be applied in spring orfall. Fall application is recommendedin most cases for more consistentcontrol. Waiting to apply nonselectiveherbicides to perennial weeds at theproper growth stage in spring maydelay alfalfa planting past theoptimum time.

Herbicides for perennial weed controlthe year before seeding alfalfa includedicamba, glyphosate, 2,4-D, Stinger,Permit, and tank mixes of these herbi-cides. Carryover from dicamba andStinger will damage alfalfa seedlingsunless they are used far enough inadvance of alfalfa planting. Consultlabels for specific plant back recom-mendations.One of the most serious perennialweed problems in alfalfa stands innorthern states is quackgrass. Fallapplication of glyphosate is moreeffective than spring application.Quackgrass should be activelygrowing when glyphosate is applied.

Weed management in the seeding yearTillage is an important part of a weedmanagement program when estab-lishing alfalfa. Thorough tillage helpsuproot existing annual weeds and setsback established perennial weeds.Final tillage should be done as nearplanting as possible to allow alfalfa ahead start on weed growth. Alfalfa in the Midwest is often plantedwith a companion crop to controlweeds and minimize soil erosion.Herbicides are seldom needed in thesesystems, especially if the small grain isharvested as silage. For direct-seededalfalfa planted in the spring, herbicidesfor weed control are usually necessary.Several herbicides are currently labeledfor use in new alfalfa seedings. Thissection describes the most commonlyused options. Performance ratings foreach herbicide are listed in table 8.

23_______________________________________________________________________________________________________________________________________ E S T A B L I S H M E N T ________________



Direct-seeded plantings—preplant-incorporated treatmentsEptam (EPTC) is a preplant-incorpo-rated herbicide that controls annualgrasses and several broadleaf weeds.Eptam must be thoroughly incorpo-rated to a depth of 2 to 3 inches.Incomplete incorporation may causestreaking and alfalfa injury or loss ofherbicide. Incorporate with a tillageimplement working the field in twodifferent directions. Eptam cantemporarily stunt alfalfa and the firstleaves may not unfold properly.Injury may be more pronouncedwhen applied under cool, wetweather, when high rates have beenapplied, or when poorly incorporated.Do not use Eptam if any atrazine wasused in the previous 12 months assevere injury may result. Do not useEptam if planting a forage grass cropwith alfalfa as grass seedlings will bekilled by Eptam.Treflan (trifluralin) is a preplant-incorporated herbicide that controlsannual grasses and some annualbroadleaf weeds. Treflan will notcontrol grass plants growing fromrhizomes, such as quackgrass. Treflanmust be incorporated to a depth of 2 to3 inches. Incorporation may bedelayed for up to 24 hours, but promptincorporation is best. Incorporate witha tillage implement according to labeldirections. Do not use Treflan if plant-ing a forage grass crop with alfalfa asgrass seedlings will be killed byTreflan. Injury rarely occurs fromTreflan applied at recommended rates.


Advanced techniquesRoundup Ready Alfalfa*

Roundup Ready alfalfa was developed by inserting the

same gene into alfalfa that was used to develop other

Roundup Ready crops. Roundup Ready alfalfa tolerates

over-the-top applications of glyphosate. Tests at the Univer-

sity of Wisconsin have shown that Roundup Ready alfalfa

can withstand repeated applications of glyphosate at high

rates for several years.

Roundup Ready alfalfa is a powerful new tool in the growers’arsenal. Weeds can now be effectively controlled in newseedings without the constraints of most current herbicides.Such constraints include narrow windows of application, rela-tively long pre-harvest intervals, risk of crop injury, requirementfor soil incorporation, and/or narrow weed control spectrum.

Ninety percent or more of the seed in Roundup Ready alfalfais glyphosate tolerant. This does mean that a small percent-age of the alfalfa seedlings (less than 10%) will die with thefirst glyphosate application. Early application of glyphosatewill remove these susceptible seedlings without affectingforage yield or stand. We do not recommend increasingseeding rates of Roundup Ready alfalfa to try to compensatefor loss of susceptible seedlings.

Roundup Ready alfalfa allows farmers to seed alfalfa withoats as a cover crop and then apply glyphosate when theoats are 6 to 8 inches tall. This practice provides the benefitsof reduced wind and water erosion and early weed controluntil the alfalfa is established and maintains the yield poten-tial of the direct seeding method.

Roundup Ready alfalfa allows more flexibility and cost effec-tiveness when controlling weeds in established stands.Glyphosate controls a broader spectrum of weeds than mostother herbicide programs, especially controlling winter annualand perennial weeds. Roundup Ready alfalfa also allowsmore flexibility in timing of herbicide application, and hasfewer harvest restrictions and fewer rotation limitationscompared with most currently available herbicides.

When rotating Roundup Ready alfalfa fields to other crops,use tillage and/or a herbicide such as 2,4-D or dicamba in thefall after the final alfalfa harvest.

*Pending approval of Roundup Ready alfalfa and labelchanges of Roundup.



Direct-seeded plantings—postemergence treatmentsBuctril (bromoxynil) is a postemer-gence contact herbicide that controlsmany common broadleaf weeds. Forbest results, treat when alfalfa has atleast four trifoliate leaves and whenweeds are 2 inches or less in heightand have no more than four leaves.Buctril gives fair to good pigweedcontrol if plants are small and activelygrowing when applied. Serious alfalfainjury may occur if the temperatureexceeds 70°F within 3 days afterapplication. Do not treat alfalfastressed by moisture shortage orexcess, insect injury, or other causes.Treated fields cannot be harvested orfed for 30 days after application.Butyrac (2,4-DB) is a postemergencesystemic herbicide that controls many

annual broadleaf weeds but is weakon larger mustards and smartweedand will not control grasses. Itsuppresses some perennial broadleafweeds. Apply when seedling weedsare small and actively growing.Correct timing is critical as control isless effective on larger weeds. Checkthe label for specific rates according toweed species and size. Treated foragecannot be harvested or grazed for 60days after application.Buctril can be tank-mixed withButyrac to improve control whenweeds in the mustard or smartweedfamily (which are sensitive to Buctril),and pigweed (which is more sensitiveto Butyrac) are present. Forage treatedwith this combination cannot beharvested or fed for 60 days afterapplication.

Poast Plus (sethoxydim) andSelect 2 EC (clethodim) are selec-tive postemergence systemic herbi-cides that control most annual grassespresent and suppress quackgrass inalfalfa. Apply to annual grasses at theheights indicated on the labels.Grasses must be actively growing forbest results. Alfalfa can be harvested 7 days afterPoast Plus treatment if the forage isgreen chopped or ensiled, and 14 daysafter treatment if harvested as dryhay. Do not harvest for hay or silageor graze within 15 days after applyingSelect. Use Poast Plus or Select tocontrol volunteer grains that emergefollowing wheat or oat harvest. Treatwhen cereals are 2 to 4 inches tall andbefore tillering has started.

25_______________________________________________________________________________________________________________________________________________________ P R O D U C T I O N ________________

Table 8. Alfalfa tolerance and herbicide effectiveness in direct seedings.(Buctril is the only herbicide registered for use on alfalfa seeded with companion crops.)

preplant incorporated ——————————— postemergence ———————————Eptam Treflan Buctril Butyrac Poast Plus Pursuit Raptor Select(EPTC) (trifluralin) (bromoxynil) (2,4-DB) (sethoxydim) (imazethapyr) (imazamox) (clethodim)

alfalfa tolerance F/G G F G G G G Ggrasses

barnyard grass G G N N G G G Gfoxtails G G P N G G G Gquackgrass P N N N F/G P/F F F/G

wild oats F P N N G F F Gbroadleaves

Eastern black nightshade P P F/G F N G G N

hoary alyssuma G N F F/G N F/G F/G N

kochia F G F/G F N G G N

lambsquarters F F G G N F G N

night-flowering catchfly F/G G F/G P N — — N

pigweed spp. F/G G F/G G N G G N

ragweed, common P N G G N F F N

smartweed spp. P P G P N G G N

velvetleaf F/G N G G N G G N

wild mustard P/F N G F N G G N

Source: Adapted from Doll, University of Wisconsin, and Becker, University of Minnesota, 2004.Abbreviations: G = good; F = fair, P = poor; N = no control. a Control ratings for annual seedlings only.



Poast Plus and Select can be tank-mixed with Butyrac and applied tonewly seeded alfalfa to control amixture of grass and broadleaf weeds.With a tank mix, the possibility ofcrop injury increases because the oilconcentrate increases Butyrac uptake.Use the rate of product as indicatedfor the weed species present. Do notadd liquid fertilizer solution orammonium sulfate when tank-mixingwith Butyrac. Treated forage cannotbe harvested or grazed for 60 daysfollowing application. It may be diffi-cult to apply this tank mix at theproper time to adequately controlboth grasses and broadleaf weedsbecause each may not be at the beststage for control at the same time. Pursuit (imazethapyr) can beapplied postemergence when seedlingalfalfa has two or more trifoliateleaves and the majority of the weedsare 1 to 3 inches in height. Pursuitcontrols many annual grass andbroadleaf weeds and suppresses someperennial weeds. Pursuit can be tank-mixed with Buctril, Butyrac, or PoastPlus. Use a labelled adjuvant and aliquid fertilizer solution such as 28%nitrogen or 10-34-0 or ammoniumsulfate to the spray solution. Follow-ing application, you must wait 30days before grazing or harvesting and4 months before replanting alfalfaback into the stand. Allow 60 daysbefore grazing or harvesting ifButyrac is included.Raptor (imazamox) is similar toPursuit in both its chemistry and useguidelines. When applied to alfalfawith two or more trifoliate leaves andto weeds that are less than 3 inchestall, Raptor controls the same weedsas Pursuit with improved control ofcommon lambsquarters and foxtailspecies. Alfafa treated with Raptor

can be harvested 20 days or moreafter application.

Companion-crop seeded plantingsBuctril (bromoxynil) can be used incompanion seedings to control severalbroadleaf weeds. It is very effective onwild mustard and common lamb-squarters. Buctril may cause seriousalfalfa injury if the temperatureexceeds 70°F within 3 days after appli-cation and if the alfalfa has fewer thanfour trifoliate leaves. Fields may beharvested 30 days after application.

Weed management in established alfalfaWeeds encroach on alfalfa as standgrowth slows due to poor fertility,disease and insect problems, andwinter injury. Removing weeds fromalfalfa seldom increases the tonnageof harvested forage. Rather, theproportion of alfalfa in the harvestedforage increases. Whether this affectsforage quality depends upon theweed species and their stage ofgrowth. Dandelions and white cockle,for instance, do not influence foragequality and animal intake whileweeds such as yellow rocket andhoary alyssum are unpalatable and

decrease animal intake. The higherfiber content of grassy weeds alsodecreases intake. Refer to table 9 for acomparison of the relative impact ofweeds on forage quality. The decision to use herbicides forweed control in established alfalfastands should be based on the degreeof the weed infestation, the type ofweeds present, and most importantly,the density of the existing alfalfastand. Alfalfa stands 3 years or oldershould have at least 55 stems persquare foot. For treatment to beeconomical, weed infestations mustbe severe enough and of species thatreduce forage quality, and alfalfastand density must be high enough torespond to the decreased competitionupon weed removal. Alfalfa does notspread into open areas, so removingweeds in thin stands often meansweed reinfestation. The cost of herbi-cide treatments such as Velpar andSencor can generally be spread over 2years because weeds will besuppressed for that length of time.Table 10 compares the herbicidesavailable for established stands. Thefollowing information describes theherbicides and when to apply them.


Table 9. Impact of common weeds on forage quality.

——————— relative seriousness ———————serious moderate slight

annual weeds cocklebur green foxtail lambsquarters

Eastern black pennycress pigweedsnightshade shepherd’s purse ragweed, common

giant foxtail velvetleaf

giant ragweed

smartweeds

yellow foxtail

perennial weeds curly dock Canada thistle dandelion

hoary alyssum quackgrass and white cockle

yellow rocket other grasses

Source: Doll, University of Wisconsin, 1998



Butyrac (2,4-DB) may be applied toestablished stands to control severalbroadleaf weeds but is weak on largermustards and smartweed and will notcontrol grasses. It gives some suppres-sion of perennial broadleaf weeds.Apply when seedling weeds are smalland actively growing. Correct timingis critical as control is less effective onlarger weeds. Check the label forspecific rates according to weedspecies and size. Treated foragecannot be harvested or grazed for 30days after application.Sencor (metribuzin) controls abroad range of annual and perennialweeds, including fair to good controlof dandelion and quackgrass. Alfalfamust be established for at least 12months before using Sencor. To avoidinjury, apply in early spring after theground is thawed and while alfalfa isstill dormant, or impregnate theherbicide onto dry fertilizer and apply

when alfalfa is less than 3 inches talland the foliage is dry. Rates vary withsoil type and weed infestation.Consult label for appropriate rates aswell as for crop rotation restrictions.Treated alfalfa may be harvested orgrazed 28 days after application.Poast Plus (sethoxydim) or Select(clethodim) may be applied to estab-lished stands of alfalfa to suppressquackgrass or control annual grasses.Treat when quackgrass is 6 to 8 inchestall and when annual grasses aresmall and actively growing. Do notapply to grass-legume mixtures asforage grasses will be stunted orkilled. Alfalfa treated with Poast Plusmay be harvested after 7 days asgreen chop or haylage and after 14days for dry hay. If treated withSelect, alfalfa can be harvested, fed, orgrazed after 15 days. Treatment can beapplied in spring or after any harvestduring the summer.

Velpar (hexazinone) controls a broadspectrum of annual and perennialweeds, including fair to good controlof dandelion and quackgrass. Alfalfashould be established for 1 year ormore prior to treatment. Apply Velparin spring to dormant alfalfa or beforenew growth exceeds 1 to 2 inches.Treating taller alfalfa will severelyinjure plants. Rates vary according toweed types present and soil type.Consult the label for specific recom-mendations. Do not graze or feedtreated hay for 30 days. Corn may beplanted 1 year after treatment; for allother crops, including alfalfa, youmust wait 2 years before planting.Fall-applied Velpar controls certainspecies (especially winter annuals)but is less effective on dandelion thanspring applications. The uncertaintyof winter survival of alfalfa alsomakes fall treatment a risky venturein most areas.

27_______________________________________________________________________________________________________________________________________________________ P R O D U C T I O N ________________

Table 10. Alfalfa tolerance and herbicide effectiveness on common weeds in established stands.

Butyrac Poast Plus Select Sencor Velpar(2,4-DB) (sethoxydim) (clethodim) (metribuzin) (hexazinone)

alfalfa tolerance F/G G G F/G F/Gannual weeds

field pennycress F/G N N G Gfoxtail spp. N G G G Gnight-flowering catchfly P N N G Gshepherd’s purse F/G N N G GVirginia pepperweed F/G N N G G

biennial weedsspotted knapweed F N N F N

perennial weedsCanada thistle P N N P Ncurly dock P N N F Fdandelion P N N F/G F/Ghemp dogbane N N N P Nhoary alyssum F N N F/G Gorange hawkweed N N N P Nquackgrass N F/G F/G F/G F/Gsowthistle, perennial P N N N Nwhite cockle P N N F Fwirestem muhly N F/G F/G P Fyellow rocket P N N F/G G

Source: Adapted from Becker, University of Minnesota, and Doll, University of Wisconsin, 2004Abbreviations: G = good; F = fair, P = poor; N = no control.




Disease management

Several diseases occur in alfalfastands that can kill seedlings, limit

yields, and shorten stand life. Theoccurrence and severity of diseasesdepends on environmental conditions,soil type, and crop management. Feweconomical control options are avail-able for diseases once they’re presentin a field, but knowing which diseasesare present can help you select resis-tant varieties for future plantings.

AnthracnoseAnthracnose occurs most often underwarm, moist conditions and causesyield losses of up to 25%. On suscepti-ble plants, stems have large, sunken,oval- to diamond-shaped lesions.Large lesions are straw colored withbrown borders. Lesions can enlargeand join together to girdle and kill oneto several stems on a plant. Girdledstems may wilt suddenly and exhibit a“shepherd’s hook.” This should not beconfused with frost damage. Deadstems are often scattered in the fieldwith straw-colored to pearly whitedead shoots. Infected crowns turnblue-black, produce fewer stems perplant, and the plant eventually dies.Moderate or higher resistance is avail-able in many varieties.

Distribution and severity

Anthracnose

severe moderate mild

The diseased crown (right) shows blue-black coloring ofanthracnose.

Straw-colored lesions on stems are indicative of anthracnose.



Aphanomyces root rotAphanomyces root rot is an importantdisease of wet soils. It stunts and killsseedlings and causes a chronic rootdisease in established plants. Infectedseedlings develop yellow cotyledonsfollowed by chlorosis of other leaflets.Roots and stems initially appear grayand water-soaked, then turn light todark brown. Seedlings becomestunted but remain upright.Aphanomyces reduces root mass onestablished plants. Nodules arefrequently absent or in some stage ofdecay. Infected plants exhibit symp-toms similar to nitrogen deficiencyand are slow to regrow followingwinter dormancy or harvest. For bestresults, select varieties with highlevels of resistance to both

aphanomyces and Phytophthora rootrot. There are two races ofaphanomyces. Most resistance is toRace 1; however, Race 2 occurs insome areas and is more virulent thanRace 1. If you plant a resistant varietyand still have the disease, select avariety with Race 2 resistance.


Aphanomyces

29_______________________________________________________________________________________________________________________________________________________ P R O D U C T I O N ________________


Infected plants lack lateral roots (from left, second and fourth pairs).

Infected seedlings develop yellow cotyledons.

Comparison of susceptible (left) and resistant (right) varieties showsstunting and slight yellowing caused by aphanomyces.




Bacterial wiltBacterial wiltBacterial wilt symptoms begin toappear in the second and third yearand may cause serious stand losses in3- to 5-year-old stands. In early stages,affected plants turn yellow-green andare scattered throughout the stand.Severely infected plants are stuntedwith many spindly stems and small,distorted leaves. Diseased plants aremost evident in regrowth after clip-ping. Cross sections of the taprootshow a ring of yellowish browndiscoloration near the outer edge.Most varieties are now resistant tothis disease.



Varying degrees of infection shown by yellowish-brown ring.

The entire plant is stunted and yellowed by bacterial wilt.



Common leaf spot and lepto leaf spotCommon leaf spot occurs primarily infirst and second cuttings and in fallregrowth of most alfalfa stands.Disease severity depends on alfalfaconditions and varietal resistance.Symptoms appear as small, brown toblack lesions—each less than 0.1 inchdiameter—that rarely grow together.On the upper leaf surface, the lesionsmay have a small raised disc in thecenter. Leaves turn yellow and fall off.The disease causes yield reductionsand lowered forage quality throughleaf loss. Severely infected fieldsshould be harvested early. Some vari-eties are moderately resistant.Distribution and severity

Common leaf spot

Lepto leaf spot attacks youngregrowth of alfalfa during spring andfall or midwinter in southern areas.Disease growth is particularly notice-able following cool, rainy periods.The lesions start as small, black spotsand enlarge to 0.1 inch in diameterwith light brown or tan centers. Thelesions are usually surrounded by ayellow, chlorotic area. Lesions oftenenlarge and grow together. Yield andquality is lost through loss of deadleaves by wind or during harvesting.Resistant cultivars are not available.


Lepto leaf spot

31________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________



Lepto leaf spot lesions have tan centers and are surrounded by ayellow halo. Lesions often enlarge and grow together.

Common leaf spot lesions are small brown to black areas that rarelygrow together.



Fusarium wiltFusarium wilt is a vascular diseasethat causes gradual stand thinning.Initially, plants wilt and appear torecover overnight. As the diseaseprogresses, leaves turn yellow thenbecome bleached, often with areddish tint on only one side of aplant. After several months the entireplant dies. Symptoms are similar tobacterial wilt but plants are notstunted. To diagnose Fusarium, cut across section of the root. The outerring (stele) of the root is initiallystreaked a characteristic reddish-brown or brick red color. As thedisease progresses the discolorationencircles the root and the plant dies.Practice good fertility and control peaaphids and potato leafhoppers toreduce the effects of this disease.Many varieties are resistant to Fusar-ium wilt.Distribution and severity

Fusarium wilt


Disease bleaches the leaves and stems on plants scattered through-out the field. Symptoms are similar to bacterial wilt but affected plantsare not stunted.

Fusarium causes a characteristic reddish-brown discoloration thatbecomes more evident as the disease progresses (left to right).




Phytophthora root rotPhytophthora root rot can killseedlings and established plants inwet or slowly drained soils. Thedisease is especially prevalent amongnew seedlings in cool, wet soils. Infec-tion occurs as plants emerge; theyappear water-soaked and thencollapse and wither. The diseaseappears on established plants inpoorly drained soils and where waterstands for 3 days or less. Plants wilt,then leaves, especially lower ones,turn yellow to reddish brown. Lesionsdevelop on the roots. In severe cases,taproots may rot off at the depth ofsoil water saturation (frequently 1 to 6inches below ground surface). Plantsmay die within 1 week of infection orlinger on with reduced root mass andgrowth rate. Often Phytophthora rootrot is not discovered until the soildries and apparently healthy plantsbegin wilting because their rotted taproots are unable to supply adequatewater. Many highly resistant varietiesare available for poorly drained soils.

Crop rotation is of little value forPhytophthora root rot control becausethe fungus can survive indefinitely inthe soil. However, good managementpractices can prolong the productivityand life of infected plants that survivethe initial infection.

1. Maintain high soil fertility topromote extensive lateral rootdevelopment above the diseasedregion of the root and to extendthe life of the plant.

2. Avoid untimely cuttings thatmight stress the plants. Heavyrains immediately after cuttingoften result in severe infections.Do not cut, for example, betweenSeptember 1 and October 15.

3. Control leaf-feeding insects, whichcan stress plants and make themmore susceptible to Phytophthora.

4. Tilling and land-leveling, if practi-cal, can reduce Phytophthora rootrot by improving surface andsubsurface drainage.


Phytophthora root rot

33________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________

As the disease progresses (left to right), lesions develop and the taprootrots off.

Stems and leaves are bleached byPhytophthora.





Root-lesion nematodesRoot-lesion nematodesRoot-lesion nematodes reduce yieldand thin stands. The parasitic nema-todes are microscopic worms thatfeed on root hairs, feeder roots, andnitrogen-fixing nodules of alfalfa.Root-lesion nematodes reduce thealfalfa plant’s ability to take up soilnutrients and fix nitrogen. Plantsappear unhealthy and stunted,usually in spotty areas within anotherwise healthy stand. Nematodepopulations can be reduced by rotat-ing to row crops or fallowing for 2months following incorporation offorage crop residue. Moderate resis-tance is available in some varieties.



Stunted plants and stand thinning caused by root-lesion nematodes.

Seedling death due to root-lesion nematodes.



SclerotiniaSclerotinia crown and stem rot is mostdamaging to seedling stands, espe-cially those seeded in late summer.The first symptoms appear in the fallas small, brown spots on leaves andstems. During the cool, wet weatherof early spring, the crown or lowerparts of individual stems soften,discolor, and disintegrate. As infectedparts die, a white, fluffy mass growsover the area and hard, black bodies,known as sclerotia, form. Thesebodies remain on the surface of thestem or become imbedded in it. Infec-tion will spread if cool, wet weatherprevails during spring, causing rapidthinning of stands. Spring plantingreduces incidence of the disease.Plowing buries sclerotia and reducesits ability to infect new plantings.Some resistance is available in somevarieties.Distribution and severity

Sclerotinia

35________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________


Arrows point to white fluffy masses at the base of a stem.

Softened and discolored stems.

Sclerotia on stem.



Spring black stemSpring black stem occurs in the north-ern United States during early springand reduces forage yield and quality.Many small, dark brown spotsdevelop on the lower leaves andstems. Leaves, especially lower ones,turn yellow, wither, and fall off.Lesions on stems enlarge and mayblacken large areas near the base ofthe plant. Severe infestations girdleand kill the stem. The plant dies wheninfection spreads to the crown androots. Cutting the stand at early stagesof maturity will reduce leaf loss anddisease prevalence. Currently avail-able varieties have variable levels ofresistance, but none are characterizedfor this disease.Distribution and severity

Spring black stem

Summer black stemSummer black stem occurs during hot,humid weather, reducing forage yieldand quality. The disease first affectsthe base of the plant and progressesup the stem, causing leaves to fall off.Leaf spots are brown with irregularmargins and often surrounded by adiffuse yellow margin. Reddish tochocolate brown oval lesions form onthe stems and merge to discolor mostof it. Early harvest may reduce losses.Currently available varieties have littleresistance.Distribution and severity

Summer black stem




Leaf lesions (left) first appear on lower leaves.

Lesions may enlarge to girdle stems andkill the plant.



Verticillium wiltVerticillium wilt can reduce yields upto 50% beginning the second harvestyear and severely shortens stand life.Early symptoms include v-shapedyellowing on leaflet tips, sometimeswith leaflets rolling along their length.The disease progresses until all leavesare dead on a green stem. Initially, notall stems of a plant are affected. Thedisease slowly invades the crown andthe plant dies over a period ofmonths. Root vascular tissues may ormay not show internal browning.Many varieties are resistant to thisdisease.

The following measures minimize thechances of introducing the fungus toan area and spreading the diseasebetween and within fields.

1. Plant resistant varieties.2. Practice crop rotation. Deep plow

Verticillium-infested fields and donot plant alfalfa for 2 to 3 years,although a highly resistant varietycould be planted sooner. Corn andsmall grains are important non-hosts. These crops should fit wellinto a rotation with alfalfa. Redclover is a questionable host, sodon’t grow red clover on Verticil-lium-infested land.

3. Harvest non-infested fields first.Then harvest infested fields at thehard-bud or early flower stage.Early harvest can limit some yieldand quality losses caused by Verti-cillium wilt and can slow thespread of the fungus in a field.


Verticillium wilt

37________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________


Leaves show early symptoms of Verticil-lium wilt. Note v-shaped yellowing andscattered bleaching.

At later stages of infection, dead leaves appear on green stems.

Browning in roots.




Insect managementAlfalfa blotch leafminerThe alfalfa blotch leafminer was firstdetected in the Midwest in 1996.Adults are small, black, hump-backedflies that emerge from overwinteringpupae located on the surface of thesoil. The first indication of their pres-ence is the appearance of numerouspinholes (from a few to over 100) in thealfalfa leaflets. These pinholes arepunctures made during egg laying, butthe adults also feed on plant materialthat oozes from the punctures. Femaleslay one to three eggs per leaflet. Smallyellow maggots hatch within the leafand begin feeding between the upperand lower leaf surfaces. As theleafminers eat their way from the baseof the leaflet toward the tip, the tunnel,or mine, they create widens as theymature. The resulting tunnels give theleaflets a blotchy appearance. Whenfully grown, the leafminers crawl outof the leaves, drop to the ground, andpupate. In the upper Midwest, asecond generation of flies emerge inmid-July, and a third generationfollows in late August.Damaged leaves have reduced proteincontent and may fall off. Significantyield loss should only occur ifdamaged leaves drop or are shakenfrom the forage during harvest.

In the upper Midwest, harvest of thefirst crop normally controls the firstgeneration. Development of thesecond and third generations,however, may not correspond asclosely with cutting schedules and thiscould lead to more extensive injury inthose cuttings. Insecticidal controlmay be warranted if at least 30% of theleaflets have pinhole injury. Delayingapplication until blotches are apparenton numerous plants will reduce insec-ticide effectiveness. Because the eggshatch over an extended period and theadults are mobile, some insecticidetrials have had marginal controlresults. Biological control of this pestis well established in the northeasternUnited States. It is anticipated thatbiological control will also be a majorcontrol factor in the Midwest as para-sitized larvae were detected inWisconsin in 1998.Distribution and severity

Alfalfa blotch leafminer

Alfalfa weevilAlfalfa weevil larvae chew and skele-tonize leaves. Large larval popula-tions may defoliate entire plants,giving the field a grayish cast.Damage normally only occurs to thefirst harvest but both larvae andadults may damage regrowth whenpopulations are high, resulting in bothyield and stand loss.Larvae are slate-colored when small,but bright green when full grown (3⁄8inch). They have a white stripe downthe back and a black head. Althoughlarvae are present from May well intothe summer, peak feeding activityfalls off by mid-June.When full grown, the larvae spinsilken cocoons on the plants, withinthe curl of fallen dead leaves, orwithin litter on the ground. Adultsemerge in 1 to 2 weeks. They are dark

Alfalfa weevil larva and feeding damage.

Tunneling damage caused by alfalfablotch leafminer larvae.

Plants severely damaged by alfalfa weevilfeeding appear grayish-brown.




gray to brown snout beetles measur-ing 3⁄16 inch in length. There is adistinct dark shield-like mark on theback. After feeding a short time, mostleave the field and enter a restingperiod that lasts until fall. In the fall,they return to the alfalfa field and laya few eggs before the onset of coldtemperatures. In northernmost states,fall egg laying is insignificant; mosteggs are laid the following spring.Begin checking alfalfa fields for signsof weevil feeding around mid-May innorthernmost states and earlierfarther south.

Treat fields when 40% of the plant tipsof the first crop show obvious signs ofdamage. This does not mean 40% defoli-ation. If damage occurs within 7 to 10days of the suggested harvest date,harvest the hay as soon as possible;otherwise spray the field as soon aspossible. Many weevil larvae arekilled during harvesting.An alternative approach for decidingwhen to treat involves comparing thecontrol costs to the forage value. Usetable 11 to find where these twovalues intersect for the number ofalfalfa weevil larvae needed to justifychemical control.

If you’ve harvested early because ofdeveloping alfalfa weevil problems,or if substantial weevil damage hasoccurred, check the stubble carefullyfor signs of damage to new growth.Some fields may fail to green-upbecause adults and larvae consumenew crown buds as fast as they areformed. Examine the stubble, the soilsurface around alfalfa plants, andunder leaf litter for larvae and adults.If they are present and if plants showno sign of regrowth within 3 or 4 daysafter harvest, spray the stubble assoon as possible. Treat also if new growth has startedand feeding damage is apparent on50% of the growth and/or you find 6to 8 weevils or more per square foot.Distribution and severity

Alfalfa weevil

39________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________

Adult weevils bear a distinctive shield-like mark on the back.Larvae are slate-colored when small but turn bright-greenwhen full grown.

Table 11. Economic thresholds for alfalfa weevil larvae inearly bud stage alfalfa.

control cost —————forage value ($/ton)—————$/acre 45 55 65 75 85 95 105 115

—————average larvae/stem—————7 4.0 3.3 2.8 2.4 2.2 1.9 1.8 1.6

8 4.6 3.6 3.2 2.7 2.4 2.2 2.0 1.8

9 5.2 4.2 3.6 3.1 2.7 2.5 2.2 2.0

10 5.8 4.7 4.0 3.4 3.0 2.7 2.5 2.2

11 6.3 5.2 4.4 3.8 3.4 3.0 2.7 2.5

12 6.9 5.6 4.8 4.2 3.7 3.3 3.0 2.7

13 7.4 6.1 5.2 4.5 3.9 3.5 3.2 2.9

Source: Peterson, Danielson, and Higley, University of Nebraska, 1993




AphidsAphids cause stunting and yellowingof alfalfa resulting in yield loss.Heavily infested plants wilt duringthe hottest parts of the days.Green pea aphids or the spottedalfalfa aphids, which are yellow andfaintly dark spotted, congregate onstems and leaves and suck plant juice.Spotted alfalfa aphids have beenuncommon in the upper Midwest formany years. Parasites and diseasekeep the pea aphid in check mostyears, though population explosionsperiodically occur. Pea aphids are amajor problem in the hot and drywestern United States. Treat peaaphids when numbers exceed 100 persweep, particularly during dryperiods.Distribution and severity

Pea aphid

Blister beetlesBlister beetles in alfalfa hay can causesickness and death in livestock,particularly horses. Blister beetlescontain cantharidin, a chemical irri-tant that can blister internal and exter-nal body tissues. Although there arefew documented cases of fatalities incattle and sheep, cantharidin-contami-nated hay is deadly to horses. Theamount of cantharidin necessary tokill a horse is 1 milligram per kilo-gram of horse weight. Blister beetlesvary in toxicity depending on thespecies. It would require 100 stripedblister beetles to kill a 1200 lb horsecompared to 1100 of the less toxicblack blister beetles.Blister beetles are a serious problem insouthern and western states, and anoccasional problem in the upperMidwest, particularly during droughtyears or the year following drought.The several species present in theMidwest vary in size and color, butare easily recognized by their elon-gated, narrow, cylindrical, soft bodies.The “neck” area is narrower than onmost beetles. Scouting is misleadingbecause the beetles tend to cluster andwill be concentrated in parts of the


Ash-gray blister beetle.

Margined blister beetle.

Striped blister beetle.

Black blister beetle.

Aphids congregate on leaves and stemsto suck plant juice.




field while absent from other parts.Sprays are generally not effectivebecause cantharidin is a very stablecompound and the dead beetles canbe picked up in the hay. Becausebeetle populations tend to buildthroughout the season, especially inthe south, horse owners shouldconsider buying first-crop and earlysecond-crop hay during high infesta-tions of blister beetle. Harvestingfields prior to flowering and main-taining weed-free stands will reducebeetle populations.Distribution and severity

Blister beetles

Clover leaf weevilClover leaf weevil larvae eat alfalfaleaves, usually beginning with thefoliage around the base of the plant.Crop injury occurs mostly before thefirst cutting, but it is usually insignifi-cant compared with the injury causedby the alfalfa weevil. Clover leafweevils are active at night and oncloudy days. During sunny days, theyhide around the base of the plant. Larvae are slate-colored when small,and bright green when full grown.They are similar in appearance toalfalfa weevil larvae except that thehead is light brown and the whitestripe down the center of the back isoften edged with pink. Full-grownlarvae are about 1⁄2 inch long.Adult clover leaf weevils are two tothree times larger than alfalfa weevils.They are 5⁄8 inch long, dark brownflecked with black, and have a lightercolored stripe extending along eachside of the wing covers. This insectnormally leaves the fields shortlyafter the first cutting and returns inlate summer to feed and lay eggsbefore winter. There is one generationper year and they overwinter mostlyas partially grown larvae.

Treatment is rarely warranted forclover leaf weevil larvae. Manage-ment of alfalfa weevils will alsocontrol this insect. However, adultclover leaf weevils can cause damageby feeding on the green stems andregrowth after the first cutting. Largepopulations can cause extensivefeeding damage, scarring the stemsand rapidly consuming new foliage asit is produced. This type of injury ismore common during dry springswhen regrowth is slow and weevilsare abundant. Treatment should beconsidered if plants do not begin toregrow in 3 to 4 days after cutting andweevils are present in the field.Distribution and severity

Clover leaf weevil

41________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________

Clover leaf weevil larvae are similarto alfalfa weevil larvae but havelight brown heads rather than black.

Adult clover leaf weevils are dark brownflecked with black.

Clover leaf weevil larvae hide around the base of theplant during sunny days, preferring to feed at night andon cloudy days.





Clover root curculioThe clover root curculio is a poten-tially serious pest of alfalfa. Althoughthis pest can be found in most alfalfafields, high populations and seriousdamage have been localized andsporadic. However, even small popu-lations may contribute to standdecline. At this time there is no reli-able method of damage prediction orcontrol.Adults are black to dark brown,blunt-snouted weevils that areapproximately 1⁄8 inch long and 1⁄16

inch wide. The surface of the beetle’sbody is deeply “punctured.” Femaleslay eggs on the lower parts of stems,on lower leaves, or on the soil surface.Larvae hatch from these eggs andenter the soil through surface cracks.There is only one generation per year.Adults lay eggs in fall or spring, andhibernate over the winter. Eggs hatchin the spring, and egg-laying isusually complete by mid-June. Newadults emerge in June and July andlive about a year.

Adult curculios injure plants bychewing the margins of leaves, creat-ing crescent-shaped notches, or bychewing the stems and leaf buds ofyoung seedlings. Feeding damage canweaken seedlings, causing poorgrowth or death. Mature plants arenot at risk unless populations areexceedingly high.Larvae do the greatest damage, andsuch damage can be cumulative overthe years that a field exists. Newlyhatched larvae feed on nodules andsmall rootlets and chew out portionsof the main root. Feeding on the mainroot leaves long brown furrows andmay partially girdle the plant. Damage from clover root curculios isbelieved to shorten stand life,contribute to winter kill, and providean avenue for entry by disease organ-isms. No commercially acceptablecontrol techniques are available.However, do not plant alfalfa backinto old, infested alfalfa standsbecause curculio damage can destroythe new stand. Also, since adultsmigrate primarily by crawling fromfield to field, avoid seeding alfalfanext to older stands. Distribution and severity

Clover root curculio

GrasshoppersGrasshoppers can overwinter as eggsor adults, depending upon thespecies. Populations tend to buildduring the season, followed by move-ment of the grasshoppers into culti-vated crops from grassy or weedyareas where they overwintered. It isimportant to detect infestations whilethe grasshoppers are small andconcentrated in overwintering sites.Several species can feed on alfalfa.Problems occur mainly in the westernUnited States and during droughtyyears in the Midwest. Grasshoppersrarely cause economic damage inmost areas of the Midwest and shouldbe considered a minor pest.Begin spot-checking overwinteringsites during June. Estimate thenumber of grasshoppers per squareyard while walking through theseareas. Insecticide use is not suggesteduntil populations reach 20 per squareyard in field margins or 8 per squareyard within an alfalfa field. Ifeconomically damaging infestationsare detected while the grasshoppersare still concentrated, spot treat thearea to protect alfalfa fields.


Long brown furrows on the taprootcaused by curculio larvae feeding.





GrasshoppersPlant bugsPlant bugs extract plant sap with theirtube-like mouths. High populationscan stunt alfalfa growth or crinkle andpucker leaves. However, these symp-toms may be caused by other factorsso be sure to positively identify theproblem before treating plants.

The two plant bugs that are particu-larly important to alfalfa productionare the tarnished plant bug and thealfalfa plant bug. The adult tarnishedplant bug is 1⁄4 inch long and brown.Nymphs are green with black spotson the back. Adult alfalfa plant bugsare 3⁄8 inch long and are light green.Nymphs are green with red eyes. Treatment is suggested if there arethree plant bug adults and/ornymphs per sweep on alfalfa that isless than 3 inches tall; treat whenthere are five or more adults and/ornymphs per sweep on taller alfalfa. Ifdamage occurs within 7 to 10 days ofthe suggested harvest date, harvestthe hay as soon as possible; otherwisespray the field as soon as possible.Distribution and severity

Plant bugs

43_______________________________________________________________________________________________________________________________________ E S T A B L I S H M E N T ________________

Crinkled leaves typical of plant bugdamage.

Adult tarnished plant bugs are1⁄4 inch long.

Alfalfa plant bugs are 3⁄8 inchlong.

Grasshoppers are best controlled when they arein field borders and before they move into thealfalfa.





Potato leafhoppersPotato leafhoppers are mid- to late-season alfalfa pests that migrate tonorthcentral and eastern states fromsouthern areas in late spring. First-cropalfalfa harvested at the proper time inthe Midwest usually escapes damage.However, subsequent crops and newseedlings should be monitored forleafhoppers.These small (1⁄8 inch), green, wedge-shaped insects suck sap from plantsand damage the phloem of leaves,restricting water and nutrient flow tothe outer tip of the leaf. This creates ayellow wedge-shaped area on the tipof leaflets. Severely damaged plantswill be stunted and chlorosis willappear on all leaves if leafhoppers arenot controlled. Damage first appearsalong the edges of fields.

Alfalfa stands suffer yield and qualitylosses before any yellowing is visible.To detect leafhoppers before symp-toms appear, scout fields using aninsect sweep net. Count adult andnymph leafhoppers in 10 sweepscovering several areas of the field. Thedecision to spray depends on thefollowing factors:

1. Whether alfalfa is a new seedingor established stand. New seed-ings are most susceptible; damagein the first year can reduce yieldfor the life of the stand. It is partic-ularly important to control potatoleafhoppers on new seedingsunder a cover crop by eitherscouting and spraying or using aresistant variety, otherwise standsmay die out.

2. Plant height. Taller plants are ableto tolerate more leafhoppers.

3. Whether or not the variety hasgreater than 50% resistance topotato leafhopper. Leafhopperpopulation growth is inhibited inhighly resistant varieties. Resistantvarieties suffer significantly lessdamage and require insecticidetreatment less frequently thansusceptible varieties.

Refer to figure 17 to determine appro-priate action to take in alfalfa fields.These spray guidelines are based onaverage costs of insecticide treatmentand average hay value. Growersshould consider altering the actionthresholds if treatment cost or hayvalue deviates greatly from average.Distribution and severity

Potato leafhoppers

Adult leafhopper (actual size 1⁄8 inch).

44 ________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________

Severely damaged plants are stuntedand chlorotic. Leafhopper burn appearsfirst as yellow wedge-shaped areas onthe tips of leaflets.


spray as soon as possible

spray if harvest is more than 7 days away

no treatment necessary

spray if less than 50% PLH resistancea

alfalfa height (inches)

lea

fho

pp

ers

/10

sw

ee

ps

72

66

60

54

48

42

36

30

24

18

12

6

0

0 2 4 6 8 10 12 14 16 18 20 22 24+

Figure 17. Economic action thresholds forcontrol of potato leafhopper (PLH) in alfalfa.

Source: Mark Sulc and Ron Hammond, The Ohio State University, 2004.



SpittlebugsSpittlebug nymphs appear in earlyMay. These soft, orange or green bugscan be found in white spittle masses inleaf axils, and later in the clumps ofnew growth at tips of stems. They suckplant juices and stunt but do not yellowthe alfalfa. Alfalfa can support atremendous population of spittlebugswithout yield loss and they usuallyhave no economic impact. Treatment issuggested if there is an average of onespittlebug per alfalfa stem. Distribution and severity

Spittlebugs

Variegated cutwormVariegated cutworm larvae feed onleaves and stems. Serious damage canoccur on regrowth after the alfalfa iscut and larvae feed under the protec-tion of drying windrows. They alsocan cut seedling plants in new stands.Larvae are variable in color, rangingfrom tan to greenish-yellow to almostblack with a row of small yellow,dagger- or diamond-shaped spotsdown the center of the back. There arethree to four generations a year.Treatment should be considered if thehay does not begin to regrow in 4 to 7days after cutting and larvae arepresent in the field.Distribution and severity

Variegated cutworm

When to rotate from alfalfa

To decide when to rotate fromalfalfa, you’ll need to evaluate

stand density and yield relative toyour needs. You’ll also want to factorin rotation requirements, farm plan,total acreage of forage needed, andability to reseed. Because most ofthese factors are farm specific, thissection focuses on the relationshipbetween stand density and yield.Alfalfa has a tremendous ability toproduce maximum yield over a widerange of stand densities. New seed-ings should have at least 25 to 30plants per square foot the seedingyear. Stands gradually thin and weedsmay invade rapidly. Weedy standsforce the choice of using herbicides,which increases production cost, or ofharvesting much lower quality forage. The decision to reseed new fields ofalfalfa should be based on the yieldpotential of the stand, ideally usingactual yields from the field. The nextbest method is to count stems whenthe alfalfa is 4 to 6 inches tall and usethe data from figure 18 to estimateyield potential (assuming drought,soil fertility, or other conditions arenot limiting yield). In the Midwest,the Northeast, and many irrigatedfields in other regions, yields oftenbegin to decline in the third year ofproduction. Fields with reducedyields still cost about the same ashigh-yielding fields. This is becausehigh-yielding fields require less herbi-cide to produce high-quality forage.Plowing down more dense stands willproduce nitrogen credits. There is alsoa rotational benefit to corn followingalfalfa: it yields 10 to 15% more thancorn following corn.

45_______________________________________________________________________________________________________________________________________ E S T A B L I S H M E N T ________________

Variegated cutworm larvae can cause seriousdamage on regrowth after alfalfa is cut.

Spittlebug froth.





46

The best time to make stand decisionsis in the fall. During the last growthperiod record stem density. Then dig arandom sampling of plants and assessroot health (see related advanced tech-nique). Typically, stands that fallbelow 40 stems per square foot orthree to four healthy plants per square

foot are no longer profitable, althoughthe critical yield range will vary withindividual farming operations.Marginal stands that are healthy maybe kept while fields with high levels ofcrown rot will decline rapidly andshould be considered for rotationalong with low yield potential fields.

________________________________________________________________________________________________________________________________________ P R O D U C T I O N ______________

Varying degrees of crown rot.

Healthy plant Some discoloration

Moderate discoloration and rot Significant discoloration and rot

Greater than 50% discoloration Dead

Advanced techniquesStand evaluation

To evaluate stands, dig several alfalfa

plants and look at the condition of the

root. This will give an idea of stand

vigor and future life span. Some crown

rot will be visible in most older stands.

Look for the number of crowns and roots

with rot and the degree of infection.

Categorize plants using a scale of 0–5

(compare to the photographs at right).

Determine the percentage of plants in

each category. Healthy stands have

fewer than 30% of the plants in cate-

gories 3 and 4.

rating winter survival

0 excellent

1 excellent

2 good

3 marginal to severe winter kill

4 severe winter kill

5 already dead

Individual plants with severe injury(greater than 50% rot) are not likely tosurvive another year. Stands with a highpercentage of these plants should beconsidered for replacement.

dry

ma

tte

r yi

eld

(t

ons/

acre

)

6

5

4

3

2

1

0

7

stems per square foot

10 20 30 40 50 60 700

n

n

n

n

n

yield = (0.10 * stems) + 0.38

Figure 18. Alfalfa stem count and yieldpotential.

Source: Undersander and Cosgrove, University of Wisconsin, 1992

0

2

4 5

3

1



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Alfalfa Management Guide—Production (2 of 3)

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