|
 Bitterweed is a yellow-flowered annual weed varying in height from a few cm up to a meter. It is erect and branches from the base. It is found mainly in the semiarid rangelands of the Southwest.
Bitterweed is a major problem of sheep throughout the Southwest. Cattle are rarely poisoned. Bitterweed is a member of the sunflower family and is closely related to pingue both in appearance and in its effects on sheep. One of the major differences is that pingue is a perennial, whereas bitterweed is an annual. Bitterweed has an extremely bitter taste and is unpalatable to livestock; however, sheep seem to develop a liking for it. It is generally a problem only when there is a shortage of other green forage. Toxicity increases with maturity or when the plant is drought stressed. The toxin is a sesquiterpene lactone (hymenoxon).
Where and When It Grows
Though bitterweed can be found through much of the southwest, it causes livestock problems principally in western Texas and eastern New Mexico. Livestock are generally poisoned in the winter and early spring when animals may graze the plant because of a shortage of other forage. Maximum plant growth occurs in early spring and early summer, but seedlings may be found at any time of the year, depending on moisture and temperature conditions.
Signs and Lesions of Poisoning
Loss of appetite and weight
Rumen atony and bloating
Depression
Weakness and irregular gait
Vomiting, salivating and coughing (green vomitus may discolor the muzzle)
Head may be elevated and back arched
Emaciation and eventual death
Congestion of liver, lungs, and abomasum
Inflammation and hemorrhage of abomasum and duodenum
How It Affects Livestock
As with many other poisonous plants, the tolerance of animals to bitterweed depends on many factors. Acute cases may result in death if large amounts are eaten rapidly. As it is generally unpalatable, this does not often occur. However, chronic poisoning where animals ingest small doses is more common. Under most grazing conditions, poisoning occurs 2-4 weeks after sheep start grazing the plant. Poisoned animals will recover if they are not allowed to eat more after the first signs of poisoning. About one percent of the animal's body weight of consumed plant has been shown to be lethal. Bitterweed irritates the digestive tract causing poisoned animals to lose their appetite. Often the rumen stops functioning and animals may show signs of abdominal pain (colic). Poisoned animals lose weight rapidly and may lag behind the flock. Post mortem examinations often show lung, heart, and kidney lesions with gastritis (irritation and inflammation of the stomach).
How to Reduce Losses
There is no treatment for the condition, although charcoal has been shown to ameliorate chronic toxicity. Animals not severely poisoned may be taken from infested pastures where they often recover within a few days if given good feed and water. Ranchers with bitterweed- infested pastures should be aware of what their sheep are eating, particularly in winter and spring months. Animals should be observed for early signs of poisoning so that affected animals can be moved to better pastures.
Bitterweed poisoning has been prevented by moderate stocking in a four-pasture deferred rotation grazing system or light continuous stocking with sheep, cattle, and goats.
Bitterweed is an annual. Research data indicate that bitterweed is effectively controlled with 2,4-D ( 0.5 kg ai/Ac), picloram (0.25 kg ai/Ac), clopyralid (0.12 kg ai/Ac), or metsulfuron (35 gm/Ac) applied from autumn to early spring before flowering when the plant is actively growing. Follow all precautions for handling herbicides | 
Printable Version
E-mail this page
