Invasive Plants
Noxious Weeds in Colorado
A serious and growing problem in the West is the invasion of non-native plant species, commonly called noxious weeds. Noxious refers to the species' aggressive behavior, which damages native Colorado plant communities or economic crops. They do not have predators so they can adapt very successfully to Colorado's environment, giving them an advantage over native species. Noxious weeds outcompete native plants for food, space, light and nutrients.
Threats to Colorado
Meadow Knapweed
Meadow knapweed is classified as a “List A” species in the Colorado Noxious Weed Act, designating it for statewide eradication. It is a fertile hybrid resulting from crossbreeding black knapweed and brown knapweed.
Purple Loosestrife
Purple loosestrife is classified as a “List A” species in the Colorado Noxious Weed Act, designating it for statewide eradication.
Yellow Starthistle
Yellow starthistle is classified as a “List A” species in the Colorado Noxious Weed Act, designating it for statewide eradication.
Invasive Plants
The Colorado Noxious Weed Program
The Colorado Department of Agriculture's Noxious Weed Program is responsible for creating and updating the Colorado Noxious Weed Rule. Stay up to speed on the Weed Rule by visiting the State Weed Program regularly. The rule changes every year. The goals of the program are to:
- Prevent the introduction of new invasive plant species
- Eradicate species with isolated or limited populations
- Contain and manage those invasive species that are well established and widespread in Colorado
The Weed Rule
A List Weeds
These weeds warrant mandatory eradication because there are very few of them in the state. The goal is to prevent these weeds from getting a stronghold in Colorado by rapidly responding and quickly controlling these species.
List B Weeds
These weeds are well established in some areas of the state but not in others. Every year, the State Weed Program writes management plans for select List B species, designating areas of the state for eradication, suppression and containment.
List C Weeds
These species are widespread throughout the State and are here to stay. They can be a high priority for Parks, due to interference with visitor experience.
Help Protect Colorado from Noxious Weeds
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Use Certified Weed Free Hay
Always use hay, straw, or mulch that has been certified weed free. Make sure that pack animals used in backcountry areas are fed hay that is certified weed-free.
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Remove Seeds
Avoid transporting weed seeds which are stuck on clothing, gear, pets, or livestock. Remove weed seeds from pack animals, before leaving an area, by brushing them thoroughly and cleaning hooves.
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Moving Livestock
Confine livestock for a day or two in a small weed-free pasture before moving them to another weed-free pasture.
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Fertilizers
Limit use of fertilizers when reseeding; their use may favor weeds over native perennial species.
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Transporting Gravel
Be extra vigilant where gravel or fill material is brought in from elsewhere; weed seeds in this material can start new infestations, and bare soil provides an ideal environment for weed establishment.
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Avoid Transporting Weeds with Your Vehicle
Restrict travel to established roads and trails whenever possible. Avoid driving in noxious weed infested areas. Inspect vehicles for weed seeds stuck in tire treads or mud on the vehicle and prevent them from being carried to unaffected areas. Don’t clean infested vehicles in weed free areas.
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Transporting Plants
Don't transport flowering plants that you cannot identify.
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Finding Noxious Weeds
If you find a small number of isolated noxious weeds that have no flowers or seeds, pull the weeds and leave them where you found them to dry out. If flowers or seeds are present, place the weeds in a plastic bag or similar container and dispose of them properly.
Find a Noxious Weed?
Help protect Colorado land by reporting new infestations of weeds.
Report a Noxious Weed
Report new infestations of known weeds (A and B list) and of those not previously found in the area (C list) to the county weed supervisor or county extension office.
Contact a County Weed Supervisor