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MANAGING BITTERWEED TO REDUCE LOSSES R. Q. Landers, Jr., Darrell Ueckert and Leo B. Merrill* Bitterweed poisoning of sheep remains a serious problem in some areas ofTexas (dark area in figure 1). Herbicide use and management can reduce animal losses.

Figure 1. Bitterweed ( odorata) problem area in . Figure 2. Mature of bittertceed in early summer shou;ing finely divided leaves and flotcer heads tdth toothed ray .

Bitterweed Signs of Poisoning An annual, cool season plant of the sunflower Sheep with acute or chronic poisoning stop eating, (composit ) family, bitterweed (Hymenoxys _odorata salivate, vomit, become depressed and w ak and Ii DC) grows in dense stands on the Edwards Plateau down most ofthe time. A green salivary di charg and and Trans-Pecos areas in Texas. Individual are stain about the ITIuzzle is COlTIlTIOn. Affect d aniITIals tightly round d clusters ranging in height froin a few often lag behind the flock and lTIay stand with backs incnes to 2 fe t (figure 2). Numerous bright yellow arched. flower h ad appear from early spring to SUlTImer. Ingestion of fresh bitterweed equival nt to ap­ Dozen , occa ionally thousands, offlower heads, pro­ proximately 1.3 percent of an aniITIal' wight was ducing 50 to 75 seeds, may grow on each plant. Plants lethal in controlled feeding studies; but onl; on -half germinate in late fall and winter, especially during this amount is required when bitterwe d dev lop wetter than av rage years on limestone-derived soils under drought conditions. Recent field studi s sug­ or after mechanical disturbance or overgrazing. gest that sheep grazing under natural conditions can Leaves are divided finely into narrow strips. The tolerate much more than 1.3 percent of th ir bod. plant tastes bitter and has a strong aromatic odor weight of bitterweed. If removed froITI a sourc of when crushed. bitterweed when signs of poisoning occur, sh p nlay recover in 7 to 10 days. Cattle and goats also are *Area Extension range specialist, professor and professor in susceptible but rarely are actually poisoned. Th toxic charge, Texas Agricultural Experiment Station at San Angelo principal is a sesquiterpene lacton call d h.­ and , respectively, The Texas A&M University System. menoxon.

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Texas Agricultural Extension Service. The Texas A&M University System. Daniel C. Pfannstiel, Director. College Station, Texas Control by Management ers and kidneys of sheep already damaged by bitter­ • Rotation and proper grazing levels weed. • Flash grazing of bitterweed at critical times Control with Herbicides • Keeping animals out of bitterweed problem areas • Spray before flowering • Drylot feeding of animals during bitterweed • Spray before dense stands are established season • Consider temperature and soil moisture • Combinations of livestock Bitterweed control with herbicide sprays depends Bitterweed poisoning can be reduced or stopped on air and soil temperatures, soil moisture, stage of by managing grazing through rotation and proper plant growth and herbicide type. Control before flow­ stocking. Pasture deferment, for example, increases ering has been successful with the ester or amine vigor of grasses and forbs that compete with bitter­ formulation of 2,4-D at rates of 1 pound acid equiva­ weed. lent per acre when temperatures and soil moisture favor bitterweed growth. For this traditional method, Flash grazing by sheep, that is, turning many air temperatures should be above 72° F. with mois­ sheep into a pa ture with bitterweed for a few days ture in clay soils about 20 to 25 percent.When air and removing them before poisoning, may reduce temperatures are less than 60° F. or when three­ bitterweed vigor and allow desirable plants to pre­ fourths of the plants are blooming, control bitterweed dominate. Several ranchers have avoided toxicity by with 2,4-D plus dicamba (3:1) or 2,4,5-T plus pic­ shifting sheep from bitterweed-infested pastures to loram. Forbs important in sheep diets, including bitterweed-free pastures in 7-day cycles. tallow weed, filaree, nuttall milkvetch and croton, are Poisoned sheep usually recover after 10 days on reduced by all herbicides. alfalfa hay. Drylot feeding with alfalfa or peanut hay may be a temporary alternative when bitterweed-free pastures are not available. Integrated Control Combining cattle, sheep and goats at moderate Herbicides can prevent localized infestations of stocking rates gr atly reduces and may eliminate bitterweed from spreading and maintain bitterweed­ losses compared with heep alone or heavily stocked free pastures where animals can be held during criti­ pastur s. A four-pasture deferred rotation system cal bitterweed periods. Spray with 2,4-D before flow­ grazed moderately with cattle, sheep and goats, was ering when temperatures are above 72° F. Picloram, stablished at Texas A&M University Agricultural or mixtures of 2,4-D and dicamba or picloram and Exp riment Station at Sonora in 1949. Despite heavy 2,4,5-T, can be sprayed after flowering when air stands ofbitterwe d, no sheep have died from poison­ temperatures are slightly lower than 60° F. ing on these rotation pastures for more than 30 years Manually clearing small patches and isolat d while annual losses on pastures heavily grazed with plants is useful, although expensive on a large scale. h p alon ha averaged 8 percent. There were no Removing plants may be necessary for many years 10 se on lightly grazed pastures stocked with cattle, before the viable seed reserve in the soil is depleted. sh ep and goats. Similar systems and stocking at the Avoid disturbing soil with machinery or excessiv Texas Range Station at Barnhart have reduced, but hoof action of grazing animals. not eliminated, death losses from bitterweed. Because bitterweed grows from seed during cool, Ranchers have consistently observed that feeding moist periods, it does not compete successfully with supplemental protein aggravates bitterweed prob­ perennial plants under proper grazing management. lems, although information from experimental feed­ Long term control depends on the vigor of desirable ing trials is conflicting. Perhaps concentrated natural range grasses and forbs encouraged through defer­ protein sources such as soybean and cottonseed meal, ment and proper stocking rates with combinations of as well as nonprotein nitrogen (urea) overwhelm liv- livestock.

Acknowledgment The authors greatly acknowledge the assistance of C. J. Scifres and M. C. Calhoun, professor and associate professor, Texas Agricultural Experiment Station, College Station and San Angelo, respectively, The Texas A&M Univer­ sity System.

Education programs conducted by the Texas Agricultural Extension Service serve people ofall ages regardless ofsocioeconomic level, race, color, sex, religion or national origin. Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States Department of Agriculture coop rating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914. 1M-4-81 RS 3-3