Noxious Weed and Invasive Species Resources

Noxious Weeds

A noxious weed is a weed that has been designated as a plant that is harmful to agricultural or horticultural crops, ecosystems, or humans or livestock. Most noxious weeds have been introduced into an ecosystem. Typically they are plants that grow aggressively, multiply quickly without natural controls, and display adverse effects through contact or ingestion.

Impacts

Noxious weeds can leave a large impact on a landscape. These plants aggressively spread and disrupt natural ecosystems by outcompeting the native plants or cultivated crops. This reduces biodiversity and reduces agricultural productivity while increasing soil erosion. Noxious weed species may also increase fire risk.

Eradication

There is no one best way to eradicate noxious weeds. Like all plants, weeds vary in how they reproduce, how they respond to herbicides, and have varying root structures. Early detection and response is important when controlling noxious weeds. In the resources below is the State of Colorado noxious weed fact sheets.

List A species in Colorado are designated by the Commissioner for eradication. Examples of species include Cypress spurge, Giant reed, Knotweeds, Myrtle spurge, Purple loosetrife, and Yellow flag iris. To view plant fact sheet, click the resources below.
List B species are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, develops and implements state noxious weed management plans designed to stop the continued spread of these species. Colorado has many List B species but some examples include Russian knapweed, salt cedar (tamarisk), Russian olive, houndstongue, and Canada thistle. For more information on these species, view the resources below.
List C species are species for which the Commissioner will develop and implement state noxious weed management plans designed to support the efforts of local governing bodies to facilitate more effective integrated weed management on private and public lands. The goal of such plans will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions that choose to require management of List C species. Examples of this include chicory, common mullein, cheatgrass, halogeton, Siberian elm, and puncturevine (source of “goatheads”).
Watchlist species that have been determined to pose a potential threat to the agricultural productivity and environmental values of the lands of the state. The Watch List is intended to serve advisory and educational purposes only. Its purpose is to encourage the identification and reporting of these species to the Commissioner in order to facilitate the collection of information to assist the Commissioner in determining which species should be designated as noxious weeds.