EM 8793 • July 2002

SudangrassG. Armah-Agyeman, J. Loiland, R. Karow, and B. Bean

Grace Armah-Agyeman, former Extension research associate, Department of Crop and Soil Science, OregonState University.

Jim Loiland, U.S. Department of Agriculture, Natural Resource and Conservation Service, Pendleton, Oregon.Russell S. Karow, Extension agronomist, Oregon State University.Brent Bean, Texas A&M University Agricultural Research and Extension Center, Amarillo.

Dryland Cropping Systems

HistorySudangrass (Sorghum bicolor L. Moench) was

introduced into Texas in the early 1900s and soonbecame established as an important pasture crop.After its introduction, many improved varieties weredeveloped. They have greater disease resistance,sweeter stems, less toxic chemical content, and moreleaves than previous varieties.

This is the same species as cultivated sorghum. Inrecent years, sorghum-sudangrass hybrids weredeveloped that produce a higher yield of forage andhave increased vigor, making the plants more resis-tant to adverse conditions. Hybrids also recover andgrow back more rapidly following harvest than theolder sudangrass varieties.

DescriptionSudangrass is a fine-stemmed, summer annual

that fits well in short rotations. Like sorghum,sudangrass is tolerant of drought and warm tempera-tures.

The plant stands 4 to 6 feet tall. The stems areabout 1⁄4 inch in diameter and have many soft leaves.The plant develops only fibrous roots and does nothave rhizomes, but a single seed can produce manystems (tillers), depending on spacing. Sudangrassplants tiller extensively and have rapid regrowth potential.

Photo courtesy of Purdue Forage Information.(www.agry.purdue.edu/ext/forages/publications/grasses/sudan.htm)

Dryland Cropping Systems2

The seed head is about 15 to 30 incheslong and about half as wide. The seed is thesame size as a wheat kernel, brown, andenclosed in dark brown, yellow, or purplesmooth hulls. The hulls stay attached to thekernel after threshing.

UsesSudangrass is grown in the United States

for pasture, grazing, green chop silage, hay, orseed. The crop is used as pasture for dairy andbeef cows, sheep, and hogs, and as a rangeplant for poultry, especially turkey.

As a pasture crop, sudangrass has a highercarrying capacity than other annual grasses orlegumes, especially in regions with hot, drysummers. Where the growing season is long,growers can make as many as five cuttings ayear.

Growers also can plant it as an emergencycrop when other forage crops have failed,which fills an important need in many regions.

Conditions for growthClimate

Sudangrass has low tolerance for cold.During cold periods, if plants are not killed,they remain dormant and resume growth onlywhen conditions are favorable. Plants cannotwithstand frosts during the growing season.

The crop grows poorly at higher altitudesdue to cool or cold weather conditions anduntimely frosts. In eastern Oregon, sudangrassgrows well in the warmer areas along theColumbia and Snake rivers and the lowerelevation of the Mid-Columbia Basin.

In periods of drought, the plant becomesdormant and resumes growth when moistureconditions improve. However, extendedperiods of drought can cause wilting.

SoilThe crop grows successfully on almost

every type of soil, but it does best on loams.Coarse, porous, sandy, or gravelly soils are

generally not good for production. Usually,soils that are good for growing sorghum arealso good for sudangrass production. Eventhough the crop is not particularly sensitive toacidic soils, when soil pH falls below 5.5, youshould add lime.

Cultural practicesSeedbed preparation

A well-prepared, firm, moist seedbed isbest, but acceptable stands can grow in grasssods, stubble, or where you use no-till.

Sorghum bicolor (L.) Moench (Sudangrass).a. Inflorescence, x 1⁄2. b. Sheath, with ligule, x 21⁄2.c. Paired spikelets, x 71⁄2. d. Cluster of spikelets, x 5.Illustration originally published in the work, TheIllustrated Flora of Illinois: Grasses: Panicum to Danthonia,Second Edition, by Robert H. Mohlenbrock. ©1973,2001 by the Board of Trustees, Southern IllinoisUniversity, reprinted by permission of the publisher.

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Seeding datePurchase seed that is adapted to your

locality. In eastern Oregon, you can plantsudangrass between May 1 and June 1. It isimportant to wait until soils are warm enoughbefore seeding, as cool soils slow growth andgive weed seeds advantage over the crop. Seedwhen soil temperatures are at least 60°F.

Late planting also is not recommended,especially if you grow sudangrass for seed. Veryhot summers or early fall rains reduce yields.

Seeding method and rateUse grain drills to seed the crop. Plug drill

holes to plant at the desired row spacing.Under high rainfall or irrigated conditions, use

Table 1*. Nitrogen recommendations for the production of summer annual grasses.

Yield goal (tons dry matter/a)3–4 5–6

Previous crop lb N per acreGood legume stand (more than 4 plants/ft2) 40 90Average legume stand (2 plants/ft2) 70 120Soybeans, corn, small grain, sorghum, grass 100 170

Table 2*. Phosphorous (P2O5) and potassium (K2O) recommendations for production of summerannual grasses.

Soil test rangeBray P1 Exchangeable K Soil test Yield goal (tons dry matter/a)(lb/a) (lb/a) level 3–4 5–6 6+

pounds per acreP2O5 K2O P2O5 K2O P2O5 K2O

0–10 0–80 Very low 100 100 120 150 130 18011–20 81–150 Low 70 70 90 120 100 14021–30 151–210 Medium 50 50 60 70 70 9031–50 211–300 High 30 30 40 50 50 6051+ 301 Very high 20 0 20 0 20 0

*Source: Kramer, F.D. and K.D. Johnson. Purdue Forage Information.http://www.agry.purdue.edu/ext/forages/publications/ay263.htm

a row spacing of 6 inches or more. Underdryland conditions, row spacings of 12 to18 inches are common. If the crop will begrazed, consider using at least a 20-inch rowspacing to allow cattle room to move in thefield without trampling the crop.

Depending on available moisture and soiltype, planting depths can range from 1 to1.5 inches. Cover seed with soil to enhancegermination.

Growers usually drill or broadcastsudangrass at a rate of 25 to 35 pounds of pure,live seeds per acre. Recommended rates fromTexas are 7 to 10 pounds per acre in 36- to42-inch rows, and 20 to 25 pounds per acrewhen using a standard grain drill. Slightly

Dryland Cropping Systems4

higher rates (8 to 12 pounds per acre and 25 to35 pounds per acre, respectively) are recom-mended for hybrids.

Generally, lower seeding rates are betterfor dry areas. Higher rates are better forirrigated plantings or where rainfall is adequate.Research has shown that total forage yield isabout the same regardless of the row spacing,because both sudangrass and its hybrids tillerextensively.

FertilizerUse soil tests to determine the crop’s

nutrient needs. Fertilizer requirements areusually similar to those of other annual grasscrops. Nitrogen (N) is the most limitingnutrient in sudangrass production. Phospho-rous moves slowly in the soil, so apply it beforeplanting or band it at seeding.

Adjust the amount of fertilizer you needbased on the previous crop. Adjust rate andtime of application of fertilizer to moisturesupply and forage needs for optimum produc-tion.

Split applications are important in orderto reduce the possibility of nitrate poisoning inanimals. Divide applications equally (depend-ing on the number of harvests) and apply aftereach grazing or harvesting operation.

Tables 1 and 2 give recommendations forfertilizer use in summer annual grass produc-tion in Indiana. Adjust these rates to suit localneeds.

Weed controlUse both cultural and chemical control

methods to control weeds. Use cultivationmethods if row spacing is adequate. Plantweed-free seed, because weed problems inannual grasses most often come from the seedsource. Buy seed from reputable dealers. Also,check the seed tag to determine percent seedpurity.

Consult the Pacific Northwest WeedManagement Handbook or your local Extensionagent for information on registered herbicides.Always read product labels for specificinstructions and restrictions for each herbi-cide.

InsectsCutworms frequently injure sudangrass,

millets, and sorghum. They are especiallyinjurious to seedlings, cutting them off aboveor below the soil surface. They are most activeat night. A full-grown cutworm is about 1 to2 inches long, smooth, and either stripedgreen, brown, or gray or mottled in color.

Grasshoppers also harm sudangrass.Eastern Oregon is especially susceptible tomigratory grasshopper attacks. Chinch bugsand greenbugs attack sudangrass in otherstates. You can spray with approved insecti-cides if these insects reach economic thresh-olds. Consult the Pacific Northwest InsectManagement Handbook or contact your localExtension agent to determine when to sprayand to find out which chemicals are approvedfor use.

Birds and mammalsPheasants and quail dig seeds out of the

ground, reducing stand establishment. Crowsand pheasants feed on seedlings. Blackbirdsand sparrows feed at seed ripening stage. Birdsare most destructive when the crop is grownfor seed.

Birds are most difficult to control. There isno single effective method. To minimizedamage, do not plant fields near timbered orscrub brush areas.

Ground squirrels, woodchucks, mice,jackrabbits, and gophers can cause consider-able harm. Field mice usually eat planted seed.Moles and pocket gophers do a lot of under-ground damage. You can use standard controlmethods for squirrrels, moles, and gophers.

DiseasesThe two major diseases affecting

sudangrass plants are leaf blights and downymildew. Leaf blights cause elongated, straw-colored lesions with reddish margins onleaves. The best control is to use resistantvarieties, if they are available. Rotations withother crops break the disease cycle.

Plants infected with downy mildew havedeformed yellowish and reddish leaves. Once

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again, use of resistant varieties is the bestcontrol method. Also, remove infected debrisfrom the fields.

Treat seed to help control kernel and headsmut.

Provide the crop optimum growingconditions to help minimize the outbreak ofdiseases.

HarvestingPasture

Graze the crop when plants are at least18 inches tall (6 to 8 weeks after seeding) toreduce the risk of nitrate poisoning. Stock thepasture enough to graze it down beforeheading begins. Graze the pasture rapidly to a6- to 8-inch stubble. Then, discontinuegrazing until growth again reaches at least18 inches high, and graze again. It usuallytakes 3 to 4 weeks for sufficient regrowth.

Consider using at least a 20-inch rowspacing to allow cattle room to move in thefield without trampling the crop.

Short rotational grazing systems workwell. Subdivide fields into three or morepastures, and graze down each pasture in 7 to10 days. Stagger the planting dates for eachpasture about 10 days apart so that grazing canbegin on each pasture when the sudangrass isat the right height.

Animals trample and feed selectivelywhen growth reaches 40 inches high orhigher. If you cannot set cattle to graze thefield at the proper time, harvest the crop forhay or silage.

Green chopThis is high-protein forage. Growers

usually feed it to dairy cattle and other high-producing livestock.

Harvest plants when they are 18 to24 inches tall. Harvest before heading, as drymatter intake and digestibility are reducedafter this stage. Feed harvested forage toanimals immediately.

HayYields are greatest when the heads reach

the soft dough stage. However, thick stems at

this stage make drying difficult, so it is best tocut before heads emerge.

SeedSeed should be uniformly mature before

harvest. Sudangrass seed heads normally donot shatter, so harvesting the crop is compara-tively easy. Use a standard combine.

Potential hazardsHydrocyanide or prussic acid poisoning

Young, actively growing leaves ofsudangrass and sorghum contain varyingamounts of cyanide, a chemical that breaksdown and releases a poison known as prussicacid or hydrocyanide (HCN) when ingested.Cyanide compounds form if the plant is understress, such as drought, light freeze, or hail.When livestock eat plants that are high in thispoison, they can die. Take the followingprecautions to avoid this problem:1. Do not graze fields until plants are at least

18 inches high. The danger of poisoning isminimal at this stage.

2. Do not graze or green chop soon after akilling frost. High levels of toxic com-pounds are produced within hours after-wards. Wait until the entire plant has drieddown. The cyanogenic compounds usuallydissipate within several days.

3. Don’t graze after a nonkilling frost forseveral days. Wait until regrowth is at least18 inches high.

4. Drought also can raise cyanogenic com-pound levels. Again, let plants dry totallybefore harvesting.

Nitrate poisoningAnimals can be poisoned if they ingest

forage containing high concentrations ofnitrates. These compounds change in thedigestive tract and are absorbed into the bloodstream, where they interfere with oxygentransport. Symptoms include labored breath-ing, muscle tremors, and staggering.

The most common cause of nitratepoisoning is using high rates of nitrogenfertilizer in one application. Stress from

drought, frost, or temperature extremes alsocauses plants to accumulate nitrates. Highestlevels are usually in the lower stems.

Take the following precautions to avoidnitrate poisoning:1. Apply N fertilizer in split application.2. Raise the cutter bar 6 to 12 inches when

harvesting to avoid the basal stalks.3. Do not graze or green chop immediately

after a killing frost or drought.4. Graze when plants are at least 18 inches

tall.

For more informationOSU Extension publicationsPacific Northwest Weed Management Handbook

(revised 2002). $35Pacific Northwest Insect Management Handbook

(revised 2002). $35To order copies of these publications, send

the complete title and series number, alongwith a check or money order for the amountlisted (payable to Oregon State University),to:

Publication OrdersExtension & Station CommunicationsOregon State University422 Kerr AdministrationCorvallis, OR 97331-2119Fax: 541-737-0817We offer discounts on orders of 100 or

more copies of a single title. Please call541-737-2513 for price quotes.

Other publications in the DrylandCropping Systems set:Garbanzo Beans (Chickpeas), EM 8791 (2002).Safflower, EM 8792 (2002).Grain Sorghum, EM 8794 (2002).

Dryland Alfalfa, EM 8795 (2002).Edible Mustard, EM 8796 (2002).

These are available online ateesc.oregonstate.edu, or contact one of thefollowing county offices:Baker, Clackamas, Crook, Gilliam, Jefferson,Josephine, Klamath, Linn, Malheur, Marion,Morrow, Sherman, Umatilla, Union, Wallowa,Wasco, Yamhill

World Wide WebYou can access our Publications and

Videos catalog and many of our publicationson the Web at eesc.oregonstate.edu

BibliographyAnderson, B. and P. Guyer. 1986. Summer

Annual Forage Grasses. Neb Guide. Univer-sity of Nebraska-Lincoln CooperativeExtension Service. G74-171-A (revised).http://www.ianr.unl.edu/PUBS/range/g171.htm

Characteristics of Sorghum and Sudangrass.1999. http://www.farminfor.org/forage/sorsudan-m.htm

Fribourg, H. 2000. Summer Annual Grasses.http://www.forages.css.orst.edu/Topics/Species/Grasses/Summer_annual/Publicati…intro.htm

Kramer, F.D. and K.D. Johnson. 1998. Produc-ing Emergency or Supplemental Forage forLivestock. Purdue University AgronomyExtension. AY-263.http://www.agry.purdue.edu/ext/forages/publications/ay263.htm

Novosad, A.C. and J.N. Pratt. 1990. Keys toProfitable Summer Annual Forage. ForageProduction. Texas A&M CooperativeExtension Service. Fact Sheet L-901.

Towne G., D. Fjell, and J. Fritz. 1992. SummerAnnual Forages. Kansas State UniversityAgricultural Experiment Station andCooperative Extension Service. MF-1036.

© 2002 Oregon State University

This publication was produced and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Exten-sion work is a cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties.

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Published July 2002