Colorado Rubberweed or Pingue (Hymenoxys richardsoni)
Colorado rubberweed (pingue) may cause serious losses principally in sheep herds in Colorado, Utah, and northern and western New Mexico. Poisoning is common in sheep, but occurs occasionally in cattle. The plant is poisonous to livestock throughout the growing season. Losses are heaviest when hungry animals are trailed through Colorado rubberweed or are placed on overgrazed ranges with heavy infestations of Colorado rubberweed.
All aboveground parts of the plant contain a poisonous sesquiterpene lactone. Animals grazing the plant may have a gradual buildup of the toxin to the level that it is harmful or lethal, or they may eat large amounts of Colorado rubberweed and be poisoned immediately.
Colorado rubberweed is a small, bushy plant about 0.5 meter high that grows on dry areas of the West. It is closely related to the annual, Hymenoxys odorata (bitter rubberweed). The stalk is thick and woody. Stem bases are covered with a woolly growth. Colorado rubberweed belongs to the sunflower family. It has golden-yellow or orange flowers that resemble asters. Woolly, cotton like fibers (not shown) are often attached at the crown of the plant.
Where and When It Grows Colorado rubberweed is a perennial that grows in arid sites at elevations of 6000 to 8000 feet. It is found mostly on mountains and foothills and grows from early spring until the first frost. It is considered an invader plant and may replace more palatable forage plants that have been overgrazed.
How It Affects Livestock Most poisoning occurs in spring or fall. The plant seems to act primarily as a depressant of the digestive tract. In most cases, the first sign of poisoning to be observed is a green froth around the mouth and nose. Sheep may die if they eat 0.25 - 0.5 kg of Colorado rubberweed daily for 1 to 2 weeks, or from one large feeding.
Signs and Lesions of Poisoning
Nausea and vomiting (area about mouth may become stained green from vomitus)
Loss of appetite
Weakness and depression
Irregular gait and trembling
Emaciation and death may occur if animals are allowed to graze this plant too long; death may not occur for some time after poisoning
Congested liver, lungs, and GI tract
Liver pale and fatty
Hyperemia and hemmorhage of upper GI tract
How to Reduce Losses Animals seldom eat toxic amounts of Colorado rubberweed if desirable forage is available. Heavy losses during trailing may be prevented by avoiding heavily infested areas. Keep hungry animals away from Colorado rubberweed ranges at all times. If sheep losses become excessive, it may be advisable to change from sheep to cattle on certain ranges. There is no known treatment for Colorado rubberweed poisoning.
If Colorado rubberweed invades a range, examine your range management program carefully. On a range that is overgrazed, the desirable forage plants are gradually crowded out. Colorado rubberweed then appears and begins to spread. Colorado rubberweed can be controlled by spraying plants in the budding stages or during active growth. Research results show that an ester of 2,4-D applied at a rate of 1 kg per acre of acid equivalent effectively controls Colorado rubberweed. Follow all precautions for handling herbicides