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Noxious weeds

King County, Washington

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

Meadow knapweed
Centaurea x moncktonii 

meadow knapweed flower - click for larger image Meadow knapweed, from Europe, is a hybrid of black and brown knapweeds. It is well adapted to western Washington, where it invades pastures, parks, lawns, industrial sites, tree farms, vacant lands, railroads and roadsides. Its foliage is coarse and tough and not generally palatable to livestock. Meadow knapweed out-competes grasses and other pasture species and is difficult to control. It threatens wildlife habitat and causes problems for Christmas tree growers. Knapweed invasions cause losses averaging up to 63 percent of available grazing forage. Meadow knapweed is also known as Centaurea pratensis, Centaurea jacea x nigra and Centaurea debeauxii subsp. thuillieri.

Legal status in King County, Washington

Class B noxious weed. Property owners in King County are required to control meadow knapweed. It is also on the Washington quarantine list (known as the prohibited plants list) 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. For more information on noxious weed regulations, see Noxious weed lists and laws.

Biology and morphology

meadow knapweed plants: click for larger imageMeadow knapweed favors moist roadsides, sand/gravel bars and river banks, irrigated pastures, moist meadows, and forest openings. It is a perennial of the sunflower family (Asteraceae) and grows from a woody crown. Upright stems branch near the middle, with leaves up to6 inches long by more than an inch wide. The lower leaves are lobed or toothed; middle and upper leaves are linear. In King County it flowers from late May to August, later if it is mowed. Its flower heads are solitary at tips of the branches. Each is about the size of a nickel, pink to purple, and much rounder than spotted knapweed heads. Bracts around the flower head are light to dark brown, with paper-fringed margin, and appear shiny and coppery when flowers are mature. Seeds are about 1/8 inch long, ivory to light brown. A short row of hairs may be present on one end.

Additional information on meadow knapweed

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

Please notify us if you see meadow knapweed 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. We map all known locations of regulated noxious weeds such as meadow knapweed in order to help us and others locate new infestations in time to control them.

Meadow knapweed photos - click thumbnail for larger image

meadow knapweed young rosette - click for larger image meadow knapweed young plant - click for larger image meadow knapweed rosette from above - click for larger image meadow knapweed preflower - click for larger image Meadow knapweed in a field - click for larger image
meadow knapweed flowers and buds - click for larger image meadow knapweed by Lake Wilderness - click for larger image meadow knapweed in bud - click for larger image meadow knapweed bud closeup - click for larger image Meadow knapweed with goats - click for larger image
meadow knapweed rosette with last years seed heads - click for larger image meadow knapweed bolting - click for larger image meadow knapweed flowering stem - click for larger image

 

Report meadow knapweed in King County, Washington

Locate meadow knapweed in King County, Washington

Related information

Related agencies


Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).