Johnson County Secondary Roads Russian Knapweed Weed

Russian Knapweed (Centaurea repens)

Description: Russian Knapweed is a creeping perennial weed, native to Eurasia, which reproduces by seed and underground rhizomes. It resembles the common garden bachelor button, of which it is a relative. The roots are extremely vigorous, spreading, extensive, and characteristically black in color. The stems are erect, 2-3 feet tall, branched at the base, ridged, and have a dense gray hair-like covering. Leaves of three shapes are found on the plant. The lower leaves are pubescent. The upper leaves are small, linear, with smooth edges. Intermediate leaves have slightly toothed margins. The leaves are pubescent. The numerous rose to purple flowers are about ½ inch wide and shaped like a flask. Flowers bloom in July and seeds are formed from July to September.

Distribution: Russian knapweed is found mainly in western Iowa. This weed grows in pastures, rangeland, roadsides, waste areas, and on neglected agricultural areas.

What’s The Problem?: Russian knapweed has properties making it a difficult weed to control: it spreads by extensive underground roots that may go to a depth of 8 feet or more, and it puts out a chemical that inhibits other species from growing near it. Left uncontrolled, russian knapweed forms dense stands, which do not allow other native plants to grow near, diminishes wildlife habitat, and reduces forage for farm animals. Russian knapweed is toxic to some animals. Horses can become addicted and in severe conditions may die. Sheep and cattle are not affected.

Management Methods: Russian knapweed must be controlled over a period of years. Large infestations may only be reduced to manageable levels, rather than total eradication. No single control method will work for russian knapweed; a combination of cultural, mechanical, and chemical controls are necessary. Cultural methods (tillage, reseeding) help as part of the weed management plan, but must be used correctly and with proper timing, as even small pieces of the root system can resprout. Due to the release of the plant inhibiting chemical put out by russian knapweed, reseeding must be accompanied by tillage, along with careful use of herbicides to stress the plant. Herbicides should be part of the management plant for this weed, but must be used at labeled rates and at times when the plant is vulnerable. Be sure to read and follow labels for specific herbicides. Consult with a weed professional prior to herbicide usage to learn specifically what herbicide may suit your needs. Remember several years of management may be necessary to reduce russian knapweed populations.

photo of Russian Knapweed

Photo couresy of Weeds of Nebraska and the Great Plains published by Nebraska Department of Agriculture

Above photos courtesy of King County, WA Noxious Weed Control Program

photo of Russian Knapweed

Photo couresy of Weeds of Nebraska and the Great Plains published by Nebraska Department of Agriculture

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