To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

King County, Washington noxious weed identification and control

Slenderflower thistle
Carduus tenuiflorus

Slenderflower thistle plantThis Class A noxious weed has a limited distribution in Washington State and has not been observed in King County. Eradication of this Class A weed is required throughout Washington State. This species is also on the Washington quarantine list (known as the prohibited plants list) (external link) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts, seeds in packets, blends or "wildflower mixes" of this species, into or within the state of Washington. Slenderflower thistle invades pastures, meadows, and fields, displacing native and/or beneficial forage species.

Additional information on annual bugloss

What to do if you find this plant in King County, Washington

Please notify us if you see slenderflower thistle growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because slenderflower thistle is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as slenderflower thistle in order to help us and others locate new infestations in time to control them.

Report slenderflower thistle in King County, Washington

Locate slenderflower thistle in King County, Washington

Related information

Related agencies


Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact a staff member at the King County Noxious Weed Control Program, please call 206-296-0290 or by reach them by email.