Noxious Weeds

“Noxious weed” means 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:

  • Aggressively invades or is detrimental to economic crops or native plant communities
  • Is poisonous to livestock
  • Is a carrier of detrimental insects, diseases, or parasites
  • The direct or indirect effect of the presence of this plant is detrimental to the environmentally sound management of natural or agricultural ecosystems.

Noxious weeds impose a wide variety of negative impacts on people, wildlife, and the environment. Livestock production and crop yields can be greatly reduced as well as adding the significant costs of weed management. Noxious weeds can also reduce the value of land when infestations are severe.

Noxious Weed Categories

Plants are prioritized as List A, B, or C species by the Colorado Department of Agriculture (CDA).

  • List A: Rare noxious weeds that must be eradicated statewide.
  • List B: Discretely distributed noxious weeds that must be eradicated, contained, or suppressed, depending on their location, to stop their continued spread.
  • List C: Widespread and well-established noxious weeds in Colorado; control is recommended by the state and may be required by local government.

Find more information on noxious weeds.

How Noxious Weeds Can be Managed

  • Biological: The use of an organism such as insects, diseases, and grazing animals to control noxious weeds; useful for large, heavily infested areas. Not an effective method when eradication is the objective, but can be used to reduce the impact and dominance of noxious weeds.
  • Chemical: The use of herbicides to suppress or kill noxious weeds by disrupting biochemical processes unique to plants.
  • Cultural: Promoting and maintaining healthy native or other desirable vegetation. Methods include proper grazing management (prevention of overgrazing), re-vegetating or re-seeding, fertilizing, and irrigation.
  • Mechanical: Manual or mechanical means to remove, kill, injure, or alter growing conditions of unwanted plants. Methods include mowing, hand-pulling, tilling, mulching, cutting, and clipping seed heads.
  • Prevention: The most effective, economical, and ecologically sound management technique. The spread of noxious weeds can be prevented by cleaning equipment, vehicles, clothing, and shoes before moving to weed-free areas; using weed-free sand, soil, and gravel; and using certified weed-free seed and feed.