Spotted Knapweed

Spotted knapweed flower.
Spotted knapweed flower.
Spotted knapweed bud.

Spotted Knapweed

Centaurea stoebe ssp. micranthos

Colorado List B - Eradication required in parts of Jefferson County

Information Sheet (PDF)

Eradication Zone Map (pdf)


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.

 Treatment Timeline


JanFebMarAprMayJuneJulyAugSeptOctNovDec
Control











Removal











Herbicide











Growth











Rosette











Vegetative











Flowering











Seed