Exotic Plants: Don't Let Them Ride Along

Noxious weeds are spreading at an alarming rate in Yellowstone National Park, where approximately 200 nonnative plant species have been identified. Those that present the most serious threat to the park include aggressive invaders such as spotted knapweed, oxeye daisy, yellow and dalmatian toadflax, St. Johnswort, and leafy spurge.

Invading, nonnative plants spread quickly, often displacing native species and disrupting local plant and animal communities. Many of these plants are not edible to native wildlife such as elk, bison, bighorn sheep, mule deer, and pronghorn antelope, and they can suffer a loss of feed. In some areas, rare plants could be lost.


Nonnative plants are spread by contaminated hay, dirty vehicles, and construction equipment. They can easily become established in disturbed habitats such as roadsides and trails. Predictably, most nonnative plant infestations in the park begin along roadsides and in developed areas.

Vehicles, trailers, and equipment used or stored in areas infested with weeds can trap noxious plant seeds between tire treads, behind license plates, or in any crack or crevice. These seeds may remain in place for long periods of time before becoming dislodged. Once construction alters a native vegetation community, traffic and maintenance activities promote weed invasion. If not detected early, weeds can become established and spread into undisturbed backcountry areas.

Hay and straw harvested from weed-infested areas can introduce weed seeds wherever they are transported. Seeds can also pass through an animal’s digestive system and be deposited miles from the trailhead.

Prevention & Control

The National Park Service uses an integrated management approach to control nonnative vegetation and prevent introduction of new species. This program combines education with applied control methods such as hand-pulling, mowing, and the application of approved herbicides. These efforts are part of a cooperative, multi-agency strategy to control weeds

Help Protect Your Park

Take the time to wash your vehicle, trailer, and equipment before leaving home. Remove all loose hay, straw, and other plant products from beds of pickup trucks and interiors of open stock trailers prior to transport. Remove weed seeds from stock by brushing them thoroughly and cleaning their hooves prior to transport. Use only certified weed-free hay. Securely wrap all hay, straw, and plant products transported through the park. Please report any weed infestations you notice to park personnel.

It’s the Law

Introducing wildlife, fish, or plants, including reproductive bodies, into the park area/ ecosystem is prohibited under regulations found at 36 CFR Sec. 1.5 (a)(2)

Transporting or hauling plant products, plant by-products, and plant waste products into or through the park is prohibited, except that securely wrapped State certified weed-free hay or hay pellets, hay cubes, or grain may be transported or used when permitted by the Superintendent. Securely wrapped or covered uncertified hay may be transported on the park portion of US Highway 191 (mile 11-31).

Riders on horseback travel through a dusty field.
Day Ride Permits

Prior to riding in Yellowstone, you must obtain a free Day Ride Permit.

Three horseback riders travel across a rolling prairie.
Coggins Test

All stock (horses, burros or mules) within Yellowstone must have a negative EIA or Coggins test within the last 12 months.

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Stock Regulations

Learn how to plan a safe, enjoyable, and low-impact trip.

Horseback riders in Yellowstone
Ride a Horse

Bring your own stock or take a guided ride.

Last updated: June 19, 2019

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Contact Info

Mailing Address:

PO Box 168
Yellowstone National Park, WY 82190-0168



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