Russian knapweed

russian knapweed flower

Russian knapweed

Arcoptilon repens

Information Sheet (PDF)


Colorado List B - Eradication required in Jefferson County

General

  • Family: Asteraceae (Sunflower)
  • Herbaceous perennial
  • May be poisonous to horses

Habitat

  • Found in pastures, rangelands, roadsides, gravel pits and grasslands
  • Prefers open, sunny locations
  • Tolerant to low temperatures and coarse soils


Plant


Vegetation

  • Leaves 1 1/2 - 4 inches long and 1/4-1/2 inches wide
  • Mature plants up to 3 1/2 feet tall
  • Stems erect and branched

Roots

  • Creeping, black, scaly

Flower

  • Color: pink to lavender
  • Season: June - August
  • Size: 3/4 to 1  inches long and about 1/4-1/2 inches wide
  • Bracts are tan, papery

Seed

  • Small with a papus

Seedling

  • Most emerge in late spring
  • Some fall germination possible under optimum conditions

Reproduction

  • Seed and vegetative means


Control


Biological

  • None - Not a control option for Eradication species

Chemical

Cultural

  • Fertilization to promote grass cover
  • Prevention - maintain health of site
  • Re-vegetation of highly disturbed sites

Mechanical

  • Burning - Not recommended; deep roots protect the plant; areas disturbed by fire  are susceptible to re-invasion due to lack of competition from desirable  plants
  • Grazing - Does not control; intensive grazing contributes to ideal habitat  conditions, helping spread; may be toxic to  livestock 
  • Mowing- Not recommended


Use all chemicals according to the manufacturer's label. No specific recommendation or endorsement is made or implied by listing methods or products.