Figure 1. Hairs present on the edge of a jointedgoatgrass leaf.Figure - PDF document

Jo Figure 1. Hairs present on the edge of a jointedgoatgrass leaf.Figure 2. Jointed goatgrass spikelets beside seedsof winter wheat.Jointed GoatgrassEcology www.jointedgoatgrass.orgointed goatgrass management in winter wheathas been difficult because the genetics and growthpatterns of these two species are similar. Knowl-edge of jointed goatgrass growth characteristicscan help producers select effective managementstrategies, as some attributes of jointed goatgrassrespond to control practices. In this bulletin, wedescribe the ecology of jointed goatgrass at vari- Figure 4. Jointed goatgrass spikelets in grain ofwinter wheat.Figure 3.Two jointedgoatgrassfrom a singlespikelet. Seeds in SoilIn wheat fields infested with jointed goatgrassthe soil contains jointed goatgrass seeds andspikelets, which together form the soil seedbank. Spikelets and seeds can invade a field inseveral ways (e.g., with crop seed at plantingtime, or transported by machinery such ascombines). After the initial invasion, seed bankincreases come mainly from jointed goatgrassplants producing seeds during the growingseason, rather than from a seed source outsidethe field boundary.When in soil, weed seeds can germinate, remaindormant, or die. Seeds can die naturally or areconsumed by microbial communities in the soilor predators such as field mice, insects, or birds.The decline of live seed numbers in the seedbank follows a typical trend (Figure 5). One yearafter entering the seed bank, more than 80%of jointed goatgrass seeds are alive. Two yearslater, approximately 30% are alive, and by thethird year, less than 5% of the original populationof jointed goatgrass seeds remain alive. Jointedgoatgrass seeds may survive longer in drier soilconditions, yet their numbers still decline morerapidly than seeds of other weed species.The rapid decline in live seeds over time explainswhy including alternate crops in rotation withwinter wheat reduces density of jointed goat-grass in future wheat. The longer intervalbetween winter wheat crops favors the naturaldecline of the seed bank. Subsequently, fewerplants infest the next winter wheat crop. Pro-ducers must control jointed goatgrass duringthis interval. Any seeds produced will replenishthe seed bank and reverse the natural declineProducers observing extensive seedling emer-gence in shallowly tilled fields often ask whethertillage helps deplete the jointed goatgrass seedbank. Under some conditions, emergence ofjointed goatgrass seedlings can double in thefirst year following tillage, compared with emer-gence in no-till fields. However, seeds buriedby tillage are protected from environmentalextremes and predators, and they survive longer.Research has shown long-term survival ofjointed goatgrass in the seed bank does not differbetween tilled and no-till systems. Increasedgermination prompted by tillage apparentlyoffsets increased mortality among seeds lyingon the soil surface in no-till.A drawback with tillage is that each operationburies crop residues and encourages erosion.In semiarid regions, crop yield, especially ofsummer annuals, is greater when crop residuesremain on the soil surface. Residues keep soilwater from evaporating, thereby holding moresoil moisture available for crop growth. Produc-ers in these regions must weigh the possible Figure 5. Longevity of live seeds of jointed goatgrass in soil. Research conducted at sites in theCentral Great Plains and Pacific Northwest, where rainfall ranged from 15 to 18 inches per year. 3 12345 Viable Seed (%)Years in SeedbankCentral Great PlainsPacific Northwest short-term benefit of tillage for managingjointed goatgrass against the detrimentaleffect of tillage on crop yield.Producers can burn postharvest crop residuesto kill jointed goatgrass seeds. Although burn-ing may help on small areas of dense infestation,two aspects of this strategy limit its generaleffectiveness. First, large quantities of crop resi-due (7,000 lbs of crop residue per acre or more)must be burned to reach lethal temperatures.Second, only jointed goatgrass seeds lying onthe soil surface are killed; seeds buried in soilare protected from the lethal heat.Seedling EmergenceJointed goatgrass generally emerges during coolweather. Peak emergence occurs from Septem-ber through early November, with a secondaryflush of seedlings emerging in late winter andearly spring. Seedlings can emerge in any of thecooler months. In one study, almost all seedlingsemerged within a 3-week period in Septemberof the first year; the following year, seedlingsemerged every month from August throughApril. Germination relates closely to precipita-tion; dry periods delay germination until morefavorable conditions develop.To encourage seedling emergence, producersmay till fields 2 to 3 weeks before planting win-ter wheat. If soil moisture is adequate, seed-lings emerge and can easily be controlled priorto planting wheat. However, this practice is notconsistently effective because precipitation iserratic in semiarid regions and tillage can rap-idly dry out the soil. Also, tillage buries seedsat various depths in soil, prolonging the seed-ling emergence period. Since seedlings of deeplyburied seeds may not emerge until after wheattrolled by tillage.Producers may delay planting winter wheat toallow the emergence of more jointed goatgrassseedlings. This approach is typically ineffectiveÑnot only because of the erratic nature of jointedgoatgrass emergence, but also because delayedplanting usually reduces winter wheat yields.This trend was demonstrated with downy brome,where delayed planting reduced downy bromedensity in winter wheat only one year out ofsix; yet winter wheat yield was reduced every year of the study due to the later planting date.Producers should emphasize other culturalpractices to manage jointed goatgrass rathermum planting period.Moldboard plowing can minimize seedlingemergence because jointed goatgrass cannotemerge if buried at depths of more than 6 inches.This approach also has negative aspects. Plow-ing damages soil health by burying crop resi-dues and reducing organic matter levels, mak-ing the soil more susceptible to erosion andless productive. This strategy may be useful onlyfor small areas of dense infestations. Becauseseeds survive longer when buried deep in soil,plowing in subsequent years will bring viableseeds back to the soil surface.An intriguing trend appeared in crop rotationstudies in the Central Great Plains. Jointedgoatgrass seed density in soil declined morerapidly in winter wheatÐsunflowerÐfallow orwinter wheatÐcornÐfallow than it did in a win-ter wheatÐproso milletÐfallow rotation. Thisdifference among rotations relates to seedlingemergence in late summer. An earlier studyfound fall emergence of jointed goatgrass wasfour times greater in corn or sunflower com-pared with emergence in proso millet or sor-ghum. These crops differ in rooting patterns;i.e., proso millet and sorghum roots developclose to the soil surface, thus drying out top-soil and preventing weed germination. Thecrops can vary in the degree to which theyinfluence jointed goatgrass germination and,subsequently, long-term seed bank levels.Plant DevelopmentDevelopment of jointed goatgrass shoots orroots resembles that of winter wheat, reflectingtheir common ancestry and genetics. One dif-ference between the two species is that anthe-sis (period of flowering) for jointed goatgrass islonger than for winter wheat. This trait enablesjointed goatgrass to adjust to environmentalstress during flowering and ensures seed pro-duction. Jointed goatgrass seeds develop rap-idly after pollination occurs. Studies showeda small percentage of seeds can germinateeven if the plant is controlled shortly afterflowering. About 50% of seeds are viable bythe early milk stage.Producers can reduce jointed goatgrass seedproduction in heavily infested wheat by spray-ing with nonselective herbicides. Although thecrop is lost, this practice prevents jointed goat-grass seed production, provided plants are killedbefore the boot stage of development. Comparedwith burning crop residues or moldboard plow-ing, this strategy is more suitable for managingsmall areas of dense infestations because it iswith jointed goatgrass seeds: livestock spreadthe seeds because the digestive system of cattle Producers can avoid thisspread of seeds by processing feed with a fine-grind hammermill, as processing injures ordestroys seeds and prevents germination.InterferenceJointed goatgrass competes with wheat foressential resources such as water, light, andnutrients. To aid producers in assessing impactof jointed goatgrass, researchers have soughtto define the relationship between jointed goat-grass density and yield loss of winter wheat.That relationship has been difficult to quantifybecause multiple factorsÑwinter wheat cultivar,density of both species, time of jointed goatgrassemergence relative to winter wheat, and envi-ronmental conditionsÑinfluence the interactionbetween jointed goatgrass and winter wheat.Research demonstrated this variability in afield trial. In one year 25 plants per square yardreduced wheat grain yield 30%. The followingyear the same plant density reduced yield less Figure 6. Yield loss of winter wheat as affected by time of emergence of jointed goatgrass. Winterwheat was planted in late September; jointed goatgrass density was 18 plants per square yard.Figure 7. Yield loss of winter wheat as affected by time of removal of jointed goatgrass. Jointedgoatgrass density was 18 plants per square yard. 0142842160 Grain Yield Loss (%)Time of Emergencedays after winter wheat March 1April 1May 1June 1Harvest Grain Yield Loss (%)Time of Removal than 5%. A general guideline for producers tograss plant per square yard reduces grain yieldapproximately 1%.A key component of interference is how weedgrowth coincides with crop growth, i.e., the ear-lier jointed goatgrass emerges relative to wheat,the more damage it causes. When jointed goat-grass emerged with wheat, 18 plants per squareyard reduced grain yield of winter wheat 27%(Figure 6). In contrast, jointed goatgrass emerg-ing 42 days after winter wheat reduced yield16%, and only 6% when jointed goatgrassemerged in the spring (March).A second component of yield loss is how longjointed goatgrass competes with winter wheat. When jointed goatgrass was removed by March1, yield loss was 5%, whereas removing jointedgoatgrass on April 1 increased yield loss to 15%(Figure 7). These yield loss trends suggest theoptimum time to control jointed goatgrass islate fall or early spring. This guideline willhelp producers using postemergent herbicides (imazamox), which controlsjointed goatgrass in imazamox-tolerant wheatcultivars.Another principle for designing managementstrategies suggests any crop or weed plantthat captures resources first gains a competi-tive advantage. In that vein, producers can takesteps to improve the competitiveness of winterwheat with jointed goatgrass. For example,banding N fertilizer with winter wheat seed atplanting reduces jointed goatgrass interference10% to 15% compared with N applied broad-cast. Banding allows winter wheat to reach Nfertilizer first.Also, winter wheat cultivars differ in their com-petitiveness with jointed goatgrass. Cultivarcharacteristics favoring wheat over jointedgoatgrass include early fall and spring growth,higher tillering capacity, and taller plants. InWashington, tall cultivars having early springgrowth reduced jointed goatgrass biomass insome years 20% to 40% compared with othercultivars. Increasing seeding rates and reduc-ing row spacing likewise give winter wheat acompetitive advantage over jointed goatgrass.Seed ProductionJointed goatgrass growing in winter wheat mayproduce anywhere from a few to more thanone to three seeds). If growing without compe-tition (e.g., in areas of winter-killed wheat),jointed goatgrass can produce 3,000 seeds ormore per plant.Seed production and flowering by jointedgoatgrass are affected by cold temperatureexposureÑa process known as vernalization.Plants are easily vernalized when establishedin the fall. Those germinating and emerging inthe spring also can be vernalized in some situ-ations. Jointed goatgrass can emerge and pro-duce viable seeds in early planted crops suchas spring wheat or barley, reducing the effec-tiveness of using spring crops as a culturalpractice to manage jointed goatgrass. A winter wheat management systemincorporating N fertilizer banded bythe wheat seed, a tall cultivar, andhigher seeding rate reduced seedproduction of jointed goatgrass 45% Ò Producers can reduce jointed goatgrass seedproduction in winter wheat by using severalcultural practices together. A managementsystem comprising 1) placing N fertilizer withtive cultivar, and 3) using a higher seeding rate(140% of conventional rates), reduced seedproduction of jointed goatgrass 45% (Figure 8).This competitive advantage was even greaterwhen jointed goatgrass emerged 3 weeks afterwinter wheat, reducing jointed goatgrass seedproduction nearly 60%. Employing a singlecultural practice has a lesser effect, e.g., band-ing N fertilizer reduced seed production only10% (Figure 8).A key component of long-term populationgrowth of jointed goatgrass may be dispersalof its seeds during harvest. In Australia, downybrome population growth and spread increased16-fold when a combine dispersed seed at har-vest. Since dense jointed goatgrass patches areoften localized in fields, harvesting these areasseparately from weed-free sections of a field willminimize seed dispersal. Cleaning combinesthoroughly after harvesting infested fields alsowill reduce spread. Figure 8. Seed production of jointed goatgrass as affected by combinations of cultural practices inwinter wheat. Nitrogen was banded with wheat seeds at planting; high seeding rate was 65 pounds peracre compared with 40 pounds per acre. 7 Placement Reduction inSeed Numbers (%)Cultural Practice Combinations N Placement+ Tall CultivarN Placement+ Tall Cultivar+ High Seeding RateEmergenceAfter Wheat 0 weeks3 weeks Although not appropriate for large field areas,eliminating small, dense areas of infestationsin fields by using nonselective herbicides willprevent dispersal of jointed goatgrass duringharvest. This strategy also helps minimizepopulation growth over years.Cultural Strategies Guidedby Jointed GoatgrassEcology Improve ManagementCertain growth characteristics of jointed goat-grass can provide the foundation for effectivemanagement. Because jointed goatgrass repro-duces only by seed, any practice that reducesseed production will slow its spread. Once afield is infested with jointed goatgrass, the firstgoal is to lower the soil seed bank density.Lengthening the interval between winterwheat crops to once every 3 or 4 years canlower jointed goatgrass seed density in soil asmuch as 70% to 90%. A second crucial step isto strengthen the winter wheat canopy usingcultural practices (competitive cultivars, nitro-gen or phosphorus placement, higher seedingrates)Ña strategy that can reduce jointed goat-grass seed production 45% to 60%. Combiningthese tactics can reduce jointed goatgrass den-sity in future wheat crops 90% to 95%.In areas where planting alternative crops is notpractical, cultural tactics that strengthen thewinter wheat canopy remain effective in mini-mizing both wheat yield loss and seed produc-tion by jointed goatgrass. Lowering the densityof jointed goatgrass also provides the addedbenefit of improving herbicide effectiveness. Copyright 2002 Washington State UniversityWSU Cooperative Extension bulletins contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product. Alternate formats of our educational materials are available request for persons with disabilities. Please contact the Information Department, College of Agriculture and Home Economics,Washington State University for more information.You may order copies of this and other publications from the WSU Bulletin office, 1-800-723-1763, or online http://pubs.wsu.eduIssued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts oMay 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations onnondiscrimination regarding race, sex, religion, age, color, creed, national or ethnic origin; physical, mental or sensory disability;marital status, sexual orientation, and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reportedthrough your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intendedPublished June 2002. X. Subject codes 244 and 364. Great PlainsCentralGreat PlainsIntermountainPacificNorthwest BestManagementPractices ProposedJointed GoatgrassPublications GeneticsAncestryGene Flow IntroductionBackgroundScope of ProblemState Contacts ResistanceCausesManagement EcologySeed BanksInterference Control TacticsCultural 1ÐColoradoÑColorado State University,Ft. Collins2ÐIdahoÑUniversity of Idaho, Moscow& Twin Falls3ÐKansasÑKansas State University,Hays & Manhattan4ÐMontanaÑMontana StateUniversity, Bozeman5ÐNebraskaÑUniversity of Nebraska,North Platte & Scottsbluff6ÐOklahomaÑOklahoma StateUniversity, Stillwater7ÐOregonÑOregon State University,Corvallis & Pendleton8ÐTexasÑTexas A&M University, Vernon9ÐUtahÑUtah State University, Logan10ÐWashingtonÑWashington State University, Pullman11ÐWyomingÑUniversity of Wyoming, Laramie 1 The National Jointed Goatgrass Research Program wasestablished in 1994 through a special grant from theUSDA Cooperative State Research, Education, andExtension Service (CSREES). This program is an integratedmulti-disciplinary effort involving 11 states and more than35 state and federal scientists. The national programreceives guidance and support from state wheatcommissions and associations across the western andMidwestern United States. Participating states areNebraska, Colorado, Kansas, Wyoming, Oklahoma, Texas,Montana, Utah, Washington, Oregon, and Idaho.Publications in this series are available online at http://www.jointedgoatgrass.org. COOPERATIVE EXTENSIONAuthors:, USDA-ARS, Brookings, SD; , Washington Wheat Commission, Spokane, WA ; Oregon State University, Pendleton, OR; , University of Nebraska, North Platte, NE; Drew Lyon, Universityof Nebraska, Scotsbluff, NE; , USDA-ARS Cropping Systems, Columbia, MO; Steve Miller, Universityof Wyoming, Laramie, WY; Frank Young, USDA-ARS, Pullman, WA; Tony White, Kansas State University, Hays, KS