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Weed & Pest

Poisonous plants create challenges on the range for cattle, sheep producers

Worland – With many cattle and sheep on the rangelands grazing in Wyoming, UW Extension Specialist Barton Stam encouraged producers to be wary of poisonous plants on the range. 

“We have to be cautious of poisonous plants,” he said.

Stam spoke during the 2014 WESTI Ag Days, held in Worland on Feb. 4-5.

In sagebrush and on rocky hillsides, Stam noted that death camas is prevalent and deadly.

“Death camas will kill just about anything – including humans, horses and cows,” he said. “Sheep are most likely to be affected because it is one of the first green plants to come up.”

The plant resembles wild onions, though the bulbous root doesn’t smell like onion. 

Another deadly plant is hallogeton, which produces sodium oxalate.

“Sodium oxalate is what causes the problems in animal metabolism,” Stam said. “Sheep are heavily impacted, even though a high calcium diet will give a higher tolerance.”

Because calcium binds to oxalate, the high calcium concentration of rangeland plants is helpful.

“In a dry lot, however, where there is nothing else to eat and the sheep get hungry, we can see problems,” Stam commented. “If sheep are hauled and dumped into loading pen or we are trailing down borrow pits, we can have problems.”

Hallogeton grows well in disturbed areas and should be watched closely.

Lupine is a native plant that is common in many areas.

“If a pregnant cow eats lupine in the 40 to 70 days of gestation range, she may have a deformed calf,” Stam said. “It results in crooked calf syndrome and cleft palates.”

While lupine can be a valuable nitrogen-fixing plant that can improve soils, it must be managed. 

In many cases, producers also have to deal with larkspur poisoning. 

“Larkspur is responsible for more cattle poisonings than any other poisonous plants,” Stam said. 

Several varieties of larkspur can be found across Wyoming, and Stam noted that on the Big Horn Mountains, in particular, tall larkspur provides a struggle for producers.

“The thing with larkspur is that there is a toxicity window,” he said. “Throughout the year, the toxicity of larkspur goes down while the palatability increases. There is a little window where it is just poisonous enough and just tasty enough that is causes death in cattle.”

Sheep have a higher tolerance for larkspur, he continued, suggesting that running sheep through Forest Service leases and mountain pastures first may help producers avoid the toxicity window.

“Larkspur can also be controlled through spraying,” Stam noted. “It is a native plant, though, and is tough to deal with.”

“A lot of our poisonous plants can be easily sprayed and killed,” Stam said. “One of the problems we have, however, is that by the time we see symptoms, it is too late.”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..