Seattle, WA Invasive Plant Rules: Prohibited Species (2026)

The State's Noxious Weed List is Organized into Three Classes of Weeds: Class A, B, and C. Class A Weeds — Class A weeds are mostly newcomers to Washington, and are generally rare. The goal is to completely eradicate them before they gain a foothold. Landowners are required to completely eradicate Class A weeds. (Eradicating weeds means getting rid of the plants altogether, including plant roots.) Class B Weeds — Class B weeds are those that are widespread in some parts of the state, but limited or absent in other parts of the state. The goal with Class B weeds is to prevent them from spreading into new areas, and to contain or reduce their population in already infested areas. The State Weed Board designates Class B noxious weeds for control in those parts of the state where they are limited or absent and threaten to invade. [...] Landowners may be required to control Class B noxious weeds, depending on how widespread the species is and/or whether the species is a local priority. Check with your County Noxious Weed Control Board for more info on which Class B species you must control. Class C Weeds — Class C weeds are often widespread, or are of special interest to the agricultural industry. The State Weed Board does not require control of Class C noxious weeds. The State and many County Weed Boards provide information on identification and best management practices for these species. A County Weed Board may require landowners to control a Class C weed.