Poisoned sheep may linger 1 to 3 weeks before dying. Cattle and sheep generally graze copperweed when other feed is scarce. Cattle are more commonly poisoned and they are likely to eat the plant in the fall when they are being trailed from summer range. Sheep are occasionally poisoned in the fall and winter by eating dry leaves that have fallen to the ground. Copperweed contains an unidentified toxin that is dangerous at all times.
Toxicity reaches a peak when the plant matures.
Leaves and stems are equally toxic. How to Reduce Losses Animals seldom eat a toxic amount of copperweed if other forage is available. To reduce losses, provide adequate forage at all times. Supplemental feeding is beneficial before animals are driven through heavily infested copperweed ranges. There is no known treatment for copperweed poisoning and research on herbicide control of copperweed is lacking.