Meadow Knapweed
Centaurea jacea x nigra  History and Impact
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 × moncktonii and Centaurea debeauxii subsp. thuillieri. As a Class B noxious weed, its control is required in King County. Biology and Morphology Meadow 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.
Meadow knapweed photos - click thumbnail for larger image
If you find meadow knapweed in King County, please notify us through our online infestation form. To find out where we have records of this weed in King County, use our interactive noxious weed map and search  for meadow knapweed. For a fact sheet on identification and control, see our meadow knapweed weed alert. For more detailed information on controlling meadow knapweed in King County, please see the meadow knapweed best management practices (259 KB Acrobat file, 37 seconds on 56K modem). For the WA State Written Findings on meadow knapweed, please follow this link to the WA State Noxious Weed Control Board and for information on distinguising between different knapweed, see the informational Selected Knapweeds of Washington (316 KB Acrobat file, 46 seconds on 56K modem).
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