MSU NEWS SERVICE
BOZEMAN – A native wildflower with a foreboding name is abundant on Montana rangelands this spring. Death camas (Zigadenus spp.), a plant that resembles wild onion, has caused at least four cattle deaths in Yellowstone County so far this year.
“Montana livestock owners may want to take extra precautions and adjust when and how pastures with death camas are grazed this year,” said Jeff Mosley, Montana State University Extension range management specialist.
The plant is highly toxic to cattle, sheep and horses during spring, especially the underground onion-like bulb. When soils are moist, livestock can pull the bulb out of the ground and ingest it. Death camas greens-up early, making it more accessible and palatable than other plants in early spring, contributing to livestock eating toxic amounts.“Toxicity is less likely if livestock turn-out can be delayed to allow other forage to grow more,” Mosley said. “Toxic levels of ingestion commonly occur in pastures where grass is in short supply.”
There is no treatment for death camas poisoning and the only way to avoid it is to minimize the concentration of the toxin in an animal’s diet.
“Death camas poisoning can be minimized by making sure livestock grazing intensity is light to moderate on rangeland with death camas,” Mosley said.
The concentration of toxins in death camas and other plants varies with weather.
“This year appears to be a year when growing conditions have caused death camas to be more toxic and more abundant than usual. Livestock owners should try to avoid spring grazing this year in pastures where death camas is abundant,” said Mosley.
Death camas usually must dominate livestock diets to reach a lethal dose. But sub-lethal doses of the plant have subtle and significant negative effects, decreasing animal weight gain and milk production and inhibiting reproduction, according to Mosley.
Some evidence indicates that death camas is more toxic to livestock during cool, stormy weather.
“The chemical structure of the toxins in death camas becomes more toxic when the barometer drops, increasing chances of livestock poisoning even when livestock don’t eat very much [of the plant],” warned Mosley.
Other evidence indicates that genetic resistance to toxic plant poisoning varies.
“Livestock owners should be cautious with death camas if they have purchased livestock from outside their herd,” Mosley said. “Livestock new to the area likely have less genetic resistance to the death camas that is growing on their rangeland.”
Death camas is difficult to control with herbicides. Dicamba and 2, 4-D can be effective when applied in early spring when plants have three to six leaves and before flowering stalks appear.
For more information or questions, contact a local MSU Extension agent or visit msuextension.org.