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Wyoming Weed and Pest Council: Yellow Starthistle Discovered in Natrona County for First Time

by Wyoming Livestock Roundup

Yellow starthistle, a highly invasive weed, was discovered on private land in Natrona County in August. 

The Natrona County Weed and Pest District (NCWP) is currently overseeing the management and eradication of the weed. Now, the area is fenced off to keep most wildlife and all livestock out.

The infestation was less than an acre, and all visible plants were pulled and removed from the area. The district estimates between 500 and 600 pounds of the weed were collected. The weeds will sun rot and ferment in a secure location on NCWP property, then be burned in the winter.

It was crucial for NCWP to remove the plant and continue toward eradication because of its negative impact on the environment. 

Yellow starthistle infestation

Yellow starthistle can quickly overwhelm native plants, which can decrease forage for livestock and wildlife, damage native plant diversity and impact recreational activities.

Additionally, the plant can cause neurological disease or death in horses if they consume it in very high amounts.

“This plant doesn’t have any competition from existing plants – no Achilles heel,” said NCWP District Supervisor Brian Connely. “Therefore, it can really decimate functioning ecosystems.”

Yellow starthistle is a prolific seed producer, and a healthy plant can produce up to 15,000 seeds, causing outbreaks to spread quickly. Because of this, NCWP plans to continually treat and monitor the area with the goal of eradicating the invasive weed.

“We’ll use all of the tools available – chemical control, biocontrol, fencing, prevention and education,” Connely stated. “We’re hoping if we can get every plant controlled, we’ll be about six to eight years from eradication.”

Stop the spread

The best way to avoid infestations is to “PlayCleanGo,” and there are six easy steps to stop the spread of invasive species.

These include cleaning shoes, clothes, packs and pets before and after exploring and staying on designated trails; cleaning horses’ hooves and feeding them weed-free certified hay before adventuring and cleaning, draining and drying watercraft and angling equipment to stop aquatic hitchhikers.

It is also advised not to move firewood – buy it where you burn it, buy certified heat-treated firewood or gather onsite when permitted.

Before traveling to new areas, inspect and clean trailers, off-road and recreational vehicles with water or compressed air to remove mud, plant parts and hidden pests.

Lastly, take the PlayCleanGo Pledge and invite family and friends to do the same at

Wyoming Weed and Pest Council is comprised of 23 weed and pest districts in the state of Wyoming. The council works closely with the Wyoming Department of Agriculture and the University of Wyoming to keep current with the latest technology and research available in the ongoing management of noxious weeds and pests.

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