Noxious Weeds

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Noxious Weeds

Most gardeners would say that any weed in their garden is a noxious weed. However, in Washington State, the term “noxious weed” has a specific legal meaning: a non-native plant designated as such by federal, state or county law as aggressive and/or injurious.

The State of Washington has enacted legislation (Chapter 17.10 RCW), which created a series of Weed Control Boards at the state, regional, and county levels. The purpose of these boards is to identify aggressive and/or injurious weeds within their jurisdictions, and to facilitate the control and removal of these weeds.

Each year, the State Noxious Weed Board adopts a State Noxious Weed List. Regional and county weed boards use this list as the basis for creating their own noxious weed lists, based on the their local weed control priorities. Washington weed control laws assigns primary responsibility for noxious weed control to the landowner – whether it is private, state, or county lands.

The Impact of Noxious Weeds

Giant Hogweed. Barbara Tokarska-Guzik, University of Silesia, Noxious weeds pose a significant threat to Washington agriculture and natural resources. Noxious weeds invade farm land and pastures, increasing the overall cost of farming and, in some cases, making land unsuitable for agriculture. Some of the noxious weeds that invade pastures are toxic to domestic animals. Noxious weeds in the natural environment may be thorny and injure wildlife, may be toxic to native wildlife species, and may crowd out native plants. The chemicals used to control noxious weeds may also damage the environment.

Aquatic noxious weeds can clog waterways, crowd out native plant species, prevent native fish from accessing breeding areas, damage or ruin commercial and recreational fishing, and make swimming dangerous.

Cutting Weeds The economic cost of controlling noxious weeds is borne by all of us, even if we live in an urban environment. Noxious weed control increases the cost of agricultural food and products. Tax money is required to remove noxious weeds from the edges of our roads. By law, noxious weeds must be controlled by parks, state forests, schools and cities, resulting in higher fees and taxes. Removing noxious weeds from our lakes and waterways, and then restoring them, is very expensive.

By controlling noxious weeds, landowners protect life and health, improve habitat for fish and wildlife, maintain native plant communities, minimize the impacts to agriculture production, and save money.

Noxious Weed Classifications

The Washington State Noxious Weed Control Board adopts a State Noxious Weed List each year. This list categorizes weeds into three major classes (A, B and C) according to the seriousness of the threat they pose to the state or a region of the state:

  • Class A weeds are non-native species with a limited distribution in Washington. Preventing new infestations and eradicating existing infestations is the highest priority. Control of these species is required by law.
  • Class B weeds are non-native species that are presently limited to portions of the state. Class B species are designated for control in regions where they are not yet widespread. Preventing infestations in these areas is a high priority. In regions where a Class B species is already abundant, control is decided at the local level, with containment as the primary goal.
  • Class C weeds are other non-native weeds found in Washington. Many of these species are widespread in the state. Long-term programs of suppression and control are a local option, depending upon local threats and the feasibility of control in local areas.

Noxious Weeds Of Greatest Local Concern

Nancy Ness, Coordinator of the Grays Harbor County Noxious Weed Control Board, provided a list of the Class B and C noxious weeds of greatest concern in our local area (All Class A noxious weeds are a high priority for control). Click on the names to get more information on each species.


Smooth Cordgrass (Spartina alterniflora).Smooth Cordgrass



Bohemian Knotweed (Polygonum bohemicum).Japanese Knotweed
Giant Knotweed (Polygonum sachalinense).
Himalayan Knotweed (Polygonum polystachyum).
Japanese Knotweed (Polygonum cuspidatum).


Orange Hawkweed (Hieracium aurantiacum).Orange Hawkweed




Herb Robert (Geranium robertianum).Herb Robert




Common Gorse (Ulex europaeus).Common Gorse. Photo by Nancy Ness.




Purple Loosestrife (Lythrum salicaria). An aquatic noxious weed.Purple Loosestrife




Parrotfeather (Myriophyllum aquaticum). An aquaticParrotfeather noxious weed.




Common Reed (Phragmites australis). An aquatic noxious weed.Common Reed




Brazilian Elodea (Egeria densa). An aquatic noxious weed.Brazilian Elodea





Further information on noxious weeds may be found at the following links:

Grays Harbor County Noxious Weed Control Board. Provides information on local noxious weed activities, local weed control programs, and links to other sites.

Pacific County Noxious Weed Control Board.

Washington State Noxious Weed Control Board (WSNWCB). Information on weed control laws, noxious weed lists, educational materials, and relevant links.

Weeds Gone Wild. Plant Conservation Alliance, National Park Service. Information on invasive plants in natural areas.

Invasive Species Program. Forest Service, USDA. A portal to Forest Service invasive species information and related management and research activities across the agency and with our many partners.

Invasive Species. Washington Native Plant Society. Discussion of issues related to invasive plant species. A joint project of The University of Georgia’s Bugwood Network, USDA Forest Service and USDA APHIS PPQ. Information and images of invasive and exotic species.

Voluntary Codes of Conduct For The Gardening Public Regarding Invasive Species. St. Louis Invasive Plant Species Workshop, March 2002.