Noxious Weeds

The aim of the Noxious Weed Program is to control noxious weeds, the non-native aggressive invaders that replace native vegetation, reduce agricultural productivity, cause wind and water erosion and pose an increased threat to communities from wildfire. We do this by preventing the introduction of new invasive species; eradicating species with isolated or limited populations and containing and managing those invasive species that are well-established and widespread.

To accomplish these goals the program coordinates the efforts of local, state and federal noxious weed managers; provides funding for local entities to carry out on-the-ground weed management projects; conducts education and outreach activities and supports similar local activities; and maintains close contact with neighboring states and counties to prevent the interstate spread of noxious weeds.

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Noxious Weed FAQs

What is a noxious weed?

According to the Colorado Noxious Weed Act, a noxious weed is an alien plant or parts of an alien plant that have been designated by rule as being noxious or has been declared a noxious weed by a local advisory board, and meets one or more of the following criteria:

  1. Aggressively invades or is detrimental to economic crops or native plant communities;
  2. Is poisonous to livestock;
  3. Is a carrier of detrimental insects, diseases, or parasites;
  4. The direct or indirect effect of the presence of this plant is detrimental to the environmentally sound management of natural or agricultural ecosystems.
Why should residents and visitors to Colorado care about Noxious Weeds?

Noxious weeds threaten valuable wildlife habitat and natural resources, cause economic hardships to agricultural producers, and are a nuisance for recreational activities. The Noxious Weed Act requires all Colorado residents to control noxious weeds using integrated methods to manage noxious weeds if the same is likely to be materially damaging to the land of neighboring landowners.

What are the designated Noxious Weeds in Colorado?

The Colorado Noxious Weed List is separated into four categories; Lists A, B, C, and the “Watch List.” The lettered lists consist of regulated species with management plans varying according to list. The “Watch List” is an unregulated list of species that may be considered noxious in Colorado once more is known about the biology and behavior of the plants.

Whom should I contact if I see a Noxious Weed or unknown weed on my property?

Contact your County Weed Manager, Colorado State University Extension office, or Conservation District. They will be able to confirm the species of the plant and give you an idea of how to treat it. If it's a List A or List B noxious weed, they will report it to the Noxious Weed Program; if it's a List C species, the county may have resources to help treat the more serious infestations.

How can I obtain a copy of Noxious Weeds of Colorado?

Copies are sold through the Colorado Weed Management Association or your county weed manager may have a copy of this guide.

How can Noxious Weeds be controlled?

There is no one best way to rid the state of noxious weeds. Weeds, like all plants, vary in how they reproduce, have varying root structures (extensive root systems or a single taproot), and how they respond to herbicides. That's why an integrated weed management approach is necessary. This approach assesses the best techniques for a given species, from a choice of manual (mowing, pulling, digging up), cultural (land management practices such as irrigation, cultivation, types of cover or crops), biological (using plant pests that are native to the source of the weed; or chemical (herbicides). Other tools and techniques can be used on larger, woody weeds such as Russian olive and tamarisk.