Species Information

• Russian knapweed (hardheads)
• Acroptilon repens (L.) DC. = Centaurea picris Pallas ex Willd. = Centaurea repens L.
• USDA Symbol: ACRE3
• Oregon Noxious Weed Designation: B
• Pictures

Identification: Perennial; blooms summer to fall. Grows up to 4 ft tall. Forms dense colonies with stems that are erect and branched. Lower leaves deeply lobed, 2 to 4 inches long; upper leaves entire or serrate. Cone-shaped flowering heads 1/4 to 1/2 in wide with one flower, pink to lavender, growing at each branchlet tip. Bracts below the flower rounded with papery margins.

Impacts: This plant is an aggressive native of Eurasia that was introduced in North America in 1898. It is found in every western state in both native range and irrigated cropland. Once established, it can overrun native grasslands as well as irrigated crops. It has dense growth and spreads entirely by fragments of its creeping rootstocks or by seed. Russian knapweed can be successfully controlled with combinations of grazing and herbicides but control programs must persist for several years.

Biological Controls: One approved biocontrol agent, a gall nematode, is established in Oregon.

Oregon Maps of Russian Knapweed Distribution

Links:

USDA Plants Database information on Russian knapweed

GRIN Database information on Russian knapweed