Russian Knapweed (Centaurea repens L.)
Russian knapweed is a deeply rooted, herbaceous perennial that spreads aggressively through an extensive rhizomatous root system. It typically grows 18–36 inches tall and produces numerous heavily branched stems arising from dark brown to black creeping roots.
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The entire plant is covered in fine, dense gray hairs, giving it a distinctive sage-gray appearance. Basal leaves are deeply notched or lobed, while stem leaves are arranged alternately and have slightly toothed margins. Leaves become smaller higher up the stem.
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Flowering occurs from early summer through fall. Flower heads are solitary at stem tips or may occur in small clusters. Buds are urn-shaped and enclosed in smooth, papery bracts. Flowers consist of tightly clustered white to pink or purple florets. Seeds are small (about 2.5 mm), oval, ivory to light brown, and have a small pappus at one end.
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Russian knapweed produces sesquiterpene lactones that make it toxic to horses, causing a neurological disorder known as “chewing disease.” It also releases allelopathic compounds into the soil, suppressing the growth of surrounding vegetation and reducing forage production.
Quick ID Guide
Life Cycle:
• Perennial
• Extensive rhizomatous root system
• Dark brown to black creeping roots
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Height:
• 18–36 inches tall
• Many branched stems
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Leaves:
• Gray-green, hairy
• Basal leaves deeply lobed
• Alternate stem leaves with slight teeth
• Smaller leaves toward top
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Flowers (Early Summer–Fall):
• White, pink, or purple
• Urn-shaped buds
• Smooth, papery bracts
• Solitary at stem tips
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Seeds:
• Small, oval
• Ivory to light brown
• Short pappus
Management Options
Prevention and cultural control practices should be emphasized to limit the spread. Use certified weed-free forage, gravel, and construction materials whenever possible to prevent the accidental introduction of weeds.
Because Russian knapweed spreads through an extensive rhizomatous root system, hand pulling or digging is not recommended, as root fragments readily resprout. Mowing alone will not eliminate established stands, but repeated mowing throughout the growing season may help reduce seed production and gradually weaken root reserves. Do not mow once seeds are present. Deep cultivation can suppress the root system but is often impractical in the rocky soils common in Sublette County.
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Effective control typically requires an integrated approach combining chemical and mechanical methods. Herbicide applications are most effective when applied to actively growing plants. Spring and fall treatments targeting rosettes are recommended, though applications made to bolting plants may also provide control. Always read and follow the herbicide label before use. Contact Sublette County Weed & Pest for assistance with product selection, rates, and application timing.
