Definition of Noxious and Invasive
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What are Noxious and Invasive Weeds?


What is a noxious weed?

The term "weed" means different things to different people.  In the broadest sense, it is any plant growing where it is not wanted. Weeds can be native or non-native, invasive or non invasive, and noxious or not noxious. Legally, a noxious weed is any plant designated by a Federal, State or county government as injurious to public health, agriculture, recreation, wildlife or property. (Sheley, Petroff, and Borman,1999) A noxious weed is also commonly defined as a plant that grows out of place and is "competitive, persistent, and pernicious." (James, et al, 1991).

Are invasive plants the same as noxious weeds?

Not necessarily, although many noxious weeds are invasive. Invasive plants include not only noxious weeds, but also other plants that are not native to this country or to the area where they are growing. The BLM considers plants invasive if they have been introduced into an environment where they did not evolve. As a result, they usually have no natural enemies to limit their reproduction and spread (Westbrooks, 1998).  Some invasive plants can produce significant changes to vegetation, composition, structure, or ecosystem function. (Cronk and Fuller, 1995).



Cronk, Q., and J. Fuller. 1995. Plant Invaders: The threat to natural ecosystems. Chapman & Hall. New York

James, L., J. Evans, M. Ralphs, and R. Child, editors.1991. Noxious Range Weeds. Westview Press. Boulder, CO.

Sheley, R.,J. Petroff, M.. Borman, 1999. Introduction to Biology and Management of Noxious Rangeland Weeds, Corvallis, OR.

Westbrooks, R. 1998. Invasive plants, changing the landscape of America: Fact book. Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW). Washington, DC.

Purple Loosestrife flower, close-up. BLM photo.

Purple loosestrife, when escaped from the garden, damages wetlands.

Purple loosestrife, growing in a field. BLM photo

Last updated: 08-27-2010