Agricultural Extension Service ...... -.----...~- P~,P& H~Utt/ P~,P& ------' MANAGING BITTERWEED TO REDUCE LOSSES

R. Q. Landers, Jr. and Darrell N. Ueckert*

Bitterweed poisoning of sheep remains a serious' problem in some areas of Texas (illustrated by shaded area in figure 1). Herbicide use and livestock management can reduce animal losses.

Figure I. Bittenoeed ( odorata) problem area in Texas. Figure 2. Mature of bitterweed in early summer showing finely divided leaves and flower heads with toothed rays.

Bitterweed Signs of Poisoning An annual, cool-season plant of the sunflower Sheep with acute or chronic poisoning stop (composite) family, bitterweed (Hymenoxys odorata eating, salivate, vomit, become depressed and weak DC) grows in dense stands on the Edwards Plateau and lie down most of the time. A green salivary and Trans-Pecos areas of Texas. Individual discharge and stain around the muzzle is common. are tightly rounded clusters ranging in height from a Affected animals often lag behind the flock and may few inches to 2 feet (figure 2). Numerous bright stand with backs arched. yellow ray and disk flowers appear from early spring Ingestion of fresh bitterweed equivalent to to summer. Dozens, often hundreds of flower heads, approximately 1.3 percent ofan animal's weight was each producing 50 to 75 seeds, may grow on each lethal in controlled feeding studies; but, only one­ plant. Plants germinate in late fall and winter, half this amount is required when bitterweed especially during wetter-than-average years on develops under drought conditions. Recent field limestone-derived soils and on mechanically studies suggest that sheep grazing under natural disturbed or overgrazed areas. Leaves are finely conditions can tolerate much more than 1.3 percent divided. The plant tastes bitter and has a strong of their body weight of bitterweed. Ifremoved from a aromatic odor when crushed. source of bitterweed at the onset of poisoning, sheep may recover in 7 to 10 days. Cattle and goats also are * Extension range specialist and professor, Texas Agricultural susceptible but rarely are actually poisoned. The Experiment Station, respectively, The Texas A&M University toxic principal is a sesquiterpene lactone called System. hymenoxon.

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Texas Agricultural Extension Service. The Texas A&M University System • College Station, Texas Control by Management this, use supplemental feed providing energy and The following list includes management techni- moderate levels of natural protein before the time ques to use in controlling bitterweed poisoning. sheep start eating bitterweed. Definitely do not give • Rotation and proper grazing levels supplemental feeds containing urea to heep • Flash grazing of bitterweed at critical times exposed to bitterweed, and high protein supple­ • Keeping animals out of bitterweed problem ments should probably not be fed to sheep already areas poisoned on bitterweed. • Drylot feeding of animals during bitterweed season Control with Herbicides • Combinations of livestock To control bitterweed with herbicides, con ider • Supplemental feeding the three items listed below. Bitterweed poisoning can be reduced or stopped • Spray before flowering by managing grazing through rotation and proper • Spray before dense stands are established stocking. Pasture deferment, for example, increases • Consider temperature and soil moisture vigor of grasses and forbs that compete with Bitterweed control with herbicide sprays depend bitterweed. on air and oil temperatures, soil moisture, tage of Flash grazing by sheep, that is, turning many plant growth and herbicide type. Control before heep into a pa ture with bitterweed for a few days flowering has been succe ful with the ester or amine and removing them before poisoning, may reduce formulation of 2,4-D at rates of 1 pound acid bitterweed vigor and allow desirable plants to equivalent per acre when temperature and oil predominate. Several ranchers have avoided toxicity moisture favor bitterweed growth. For thi by shifting sheep from bitterweed-infested pastures traditional method air temperatures should be above to bitterweed-free pastures in 7-day cycles. 72° F. with 20 to 25 percent soil moisture in clay Poisoned sheep u ually recover after 10 days on soils. When air temperatures are less than 60° F. or alfalfa hay. Drylot feeding with alfalfa or peanut hay when three-fourths of the plants are blooming, may be a temporary alternative when bitterweed-free control bitterweed with 2,4-D plus dicamba (3:1), pastures are not available. picloram, 2,4-D plus picloram (4:1) or 2,4,5-T plus Combining cattle, sheep and goats at moderate picloram. Forbs important in livestock diets, stocking rates greatly reduces and may eliminate including tallow weed, filaree, nuttall milkvetch losses compared with sheep alone on heavily stocked and croton, are also controlled or suppressed by th.e pastures. A four-pasture deferred rotation system herbicides. grazed moderately with cattle, sheep and goats was Integrated Control e tablished by the Texas A&M University Agricul­ Use herbicides to prevent localized infestation of tural Experiment Station at in 1949. Despite bitterweed from spreading and to maintain heavy stands of bitterweed, no sheep have died from bitterweed-free pastures where animals can be h ld poi oning on these rotation pastures for more than during critical bitterweed periods. 30 years, whereas annual losses on pastures heavily Manually clearing small patches and i olated grazed with sheep alone have averaged 8 percent. plants is useful, although expensive on a large cale. There were no 10 es on lightly grazed pastures Removing plants may be necessary for many year sto ked with cattle, sheep and goats. Similar systems before the viable seed reserve in the soil is depleted. and stocking at the Texas Range Station at Barnhart Avoid disturbing soil with machinery or exce sive have reduced, but not eliminated, death losses from hoof action of grazing animals. Avoid spreading bitterweed. seeds into bitterweed-free areas on tires and Ranchers have consistently observed that feeding undercarriages of vehicles or equipment. upplemental protein aggravates bitterweed pro­ Because bitterweed grows from seed during cool, blems. This observation is supported by the fact that moist periods, it does not compete succes fully high protein diets are detrimental in situations within good stands of vigorous perennial plants where there is impairment of kidney and liver under proper grazing management. Long-term functions. which occurs in bitterweed poisoning. control depends on the vigor of desirable range The problem would be even more severe if a portion grasses and forbs encouraged through deferment and of the protein in the supplement were derived from a proper stocking rates with combinations of nonprotein nitrogen source, such as urea. Becauseof livestock.

Acknowledgment The author greatly acknowledge the assistance of C.]. cifres, Leo B. Merrill and M.C. Calhoun, profe or, retired professor and associate professor, Texas Agricultural Experiment Station, CoIl ge Station, Sonora and San Angelo, respectively, The Texas A&M University System. educational programs conducted by the Texas Agricultural Extension Service senle people of all ages regardless of socioeconomic level. race, color, sex, religion, handicap or national origin. Issued in funherance of Cooperalive EXlension Work in Agricullure and Home Economics, AClS of Congress of May 8, 1914, as amended, and June 30, 1914, in ooperalion wilh lhe Uniled Slale Depanmenl of Agricullure. Zerle L. Carpenter, Direclor:, Texas Agricullural Exlen ion ervice, The Texas A&M UniversilY Syslem. 2M-4-85, Revision R 3-3