Spotted Knapweed

spotted knapweed flower
spotted knapweed flower close up
spotted knapweed bud

Spotted Knapweed

Centaurea stoebe aka C.maculosa , C. biebersteinii

Information Sheet (PDF)


Colorado List B - Eradication required in Jefferson County

General

  • Family: Sunflower (Asteraceae)
  • Introduced to North America in the late 1800s or early 1900s
  • Native Range: Central Europe
  • Very invasive herbaceous, long-lived biennial (short-lived perennial)


Habitat

  • Causes serious decline in forage and crop production
  • Found in meadows, pastures, roadsides and sandy or gravelly sites
  • Heavily infested areas will probably need to be reseeded once the plant is controlled
  • Soil erosion is sometimes a problem because roots don’t hold soil as well as native vegetation


Plant


Vegetation

  • 1 to 20 upright stems, 1 to 3 feet long
  • Forms rosettes the first year and bolts in the spring of the second growing season (May to June)
  • Plant is 1 to 4 feet tall
  • Rosette leaves are 6 inches long and deeply lobed


Roots

  • Tap root


Flower

  • Bracts have black tips, fringed edges; no terminal spine
  • Color: pink or purple
  • Flowering occurs summer through fall (late June to October)
  • Single three quarters to 1 inch wide


Seed

  • Each plant can produce as many as 40,000 seeds
  • Most seeds fall within 3 feet of the plant
  • Seeds can stay dormant for 8 years


Seedling

  • Seeds germinate in spring or fall


Reproduction

  • Seed


Control


Biological

  • None; biological control is not an option under eradication


Chemical


Cultural

  • Prevention – maintain health of site
  • Removal - make sure entire root is removed; must be repeated as new  plants germinate; any flowers must be bagged and disposed of at a  landfill
  • Re-vegetation - maintaining good ground cover helps prevent re-infestation


Mechanical

  • Burning - N/A
  • Grazing - N/A
  • Mowing - Mow before flowering, followed with herbicide treatment


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