Spotted Knapweed
Centaurea stoebe (syn. C. biebersteinii, C. maculosa)

History and Impact

This exotic invader from Europe is a member of the sunflower family (Asteraceae). Spotted knapweed threatens wildlife habitat, pastures, and grasses, and causes problems for Christmas tree growers. Knapweed invasions cause losses averaging up to 63 percent of available grazing forage. Many spotted knapweed infestations start on rights of-way or from infested gravel or fill. As a Class B noxious weed, control is required in King County, Washington.

Biology and Morphology

Spotted knapweed is a perennial with several branched upright stems growing from a stout taproot; usually to 5 feet tall. Leaves become smaller as they advance up the stem; heads of pink to purple (sometimes white) flowers grow at the ends of the branches; excluding flowers, the heads are about 1/4" in diameter by 1/2" tall. Bracts around the flower heads have obvious vertical veins below the black triangular spot on the bract tip. It flowers continuously from early summer into the fall, as long as moisture and temperatures permit.

Further Information

For information on spotted knapweed identification and control, please download our spotted knapweed weed alert (373 KB Acrobat file).

If you find spotted knapweed in King County, Washington please notify us through our online infestation form.

To find out where we have records of this weed in King County, Washington use our interactive noxious weed map and search for spotted knapweed.

For more information about spotted knapweed, please see the Washington State Noxious Weed Control Board website.

For detailed information on managing spotted knapweed in King County, please read the spotted knapweed best management practices (187 KB Acrobat file, 27 seconds on 56K modem) and the informational Selected Knapweeds of Washington (316 KB Acrobat file, 46 seconds on 56K modem).

Spotted knapweed photos - click thumbnail for larger image