Protect against livestock losses from toxic larkspur; 2 ways: Manage around the weed or control it |

Protect against livestock losses from toxic larkspur; 2 ways: Manage around the weed or control it

Brandon Greet, Andrew Kniss and Brian Mealor | University of Wyoming
Tall larkspur is a native perennial weed that can cause cattle producers significant economic losses. (Photo courtesy of the University of Wyoming)

Throughout the drought and other production pressures, poisonous plants still need to be dealt with.

Tall larkspur is a native perennial weed that can cause cattle producers significant economic losses.

While generally safe for sheep, tall larkspur takes its toll on cattle through death losses and decreased production due to poisonous alkaloids.

Mitigating tall larkspur includes managing around their toxicity or controlling them.

Window of Toxicity

Time of grazing is the most important management practice.

Tall larkspur has what is called a “window of toxicity.”

If grazed inside this window, significant death loss will likely occur.

Proper identification of tall larkspur is important because tall larkspur has a different window of toxicity than short or plains larkspurs.

Prior to the window, tall larkspur plants are short and in the vegetative growth stage.

The plants are extremely poisonous but have very low palatability.

The bitter taste will keep cattle from consuming deadly amounts.

Palatability becomes acceptable for cattle when the plants enter the flower stage.

This is the most important time to keep cattle from grazing pastures infested with tall larkspur.

Later, during the seed stage, tall larkspurs will senesce, or dry up.

Once completely brown, they are no longer poisonous to cattle.

The alkaloids have mostly been pulled into the roots for winter dormancy.

How to Manage

To completely prevent death loss due to tall larkspur and allow flexibility in grazing management, remove the plants.

If there is a small patch, hand pulling and removing from the pasture is practical.

This takes a lot of labor and persistence but doesn’t require chemicals and can save money.

However, larger infestations must be controlled other ways.

In the past, broadcast applications of Tordon (picloram) and Escort (metsulfuron-methyl) and spot applications of Roundup (glyphosate) have shown good efficacy against these plants.

Applications of Escort in the spring have generally shown the best results.

However, there are new chemicals to consider in the near future.

DuPont is putting its new, active ingredient, aminocyclopyrachlor (the active ingredient in Imprelis), in several chemicals. Although not yet labeled for rangeland use, these chemicals have shown good efficacy for tall larkspur control and, at 2012 prices, would be cheaper than Tordon or Escort.

Be Persistent

Know what the effect could be on grazing when using any chemical means of control.

Any of these chemicals can reduce grass production in the short term.

Many times, this loss is worth reducing the tall larkspur presence.

Persistence is the key for any weed control program.

Chemical applications will likely have to be repeated, and modifications to the grazing programs during these applications may be necessary.

Increased toxicity of tall larkspur plants is likely immediately after herbicide application.

Ranchers need to wait until plants are completely desiccated before the treated area is grazed.

Brandon Greet is a University of Wyoming Extension educator based in Washakie County and also serving Big Horn, Hot Springs, Park counties and the Wind River Reservation. He can be reached at 307-347-3431 or at

Andrew Kniss is an assistant professor in the Department of Plant Sciences in the University of Wyoming College of Agriculture and Natural Resources. He can be reached at 307-766-3949 or at

Brian Mealor is an assistant professor in the department and is the UW Extension weed specialist. He can be contacted at 307-766-3113 or at ❖


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