Russian Knapweed (State designated weed)

Russian Knapweed (State designated weed)

  • Centaurea repens
  • Asteraceae (Sunflower family)

Russian knapweed is a native of Eurasia, probably introduced in North America about 1898. It is now widely established in the Western U.S. and heavily infests some regions of Fremont County. The species forms colonies in cultivated fields, orchards, pastures and along roadsides.

Growth Habit: Upright perennial herb, up to 3 feet tall, often grows in dense clumps. Grayish color.

Leaves: Alternate, simple, of several types: Upper leaves are small, narrow, unbroken edges. Stem leaves are intermediate in size with slightly toothed margins. Basal leaves are deeply notched.

Stems: Numerous branches, each ending with a single flower.

Flowers: Single, terminal, white to lavender, cone-shaped, scaly seed head. Many pearly bracts form with rounded or acute papery margins. Flowering occurs from June to September and seed is produced in late summer to early fall.

Roots: Dark brown to black and heavily scaled. Taproot can grow 8 feet long or more, and a system of creeping horizontal roots produces many more plants.

Other: Russian knapweed might be referred to as a “steam roller” on the noxious list because it has the ability to completely overrun an area if not contained. Russian knapweed is poisonous to horses (affecting the liver) and is not grazed by other livestock if another choice exists.

Status: State Designated Noxious Weed, Category 3 Fremont County. Regional. No tolerance of further spread, control and management of current infestations and aggressive control in areas otherwise free of these weeds.

Control: Chemical controls are typically more effective than mechanical. The Russian knapweed gall midge, a biological control, has shown some effectiveness in Fremont County. A 40 percent cost share on chemicals is available throughout the county for control of this weed. As funding allows, an 80 percent cost share may be available in some areas through a Russian Knapweed Special Management program. Contact your local weed and pest office for further treatment recommendations.

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