Plumeless Thistle

plumeless thistle flower
plumeless thistle habit
plumeless thistle rosette

Plumeless Thistle

Carduus acanthoides

Information Sheet (PDF)


Colorado List B - Eradication required in Jefferson County


General

  • Biennial (short-lived perennial)
  • Family: Sunflower (Asteraceae)
  • Herbaceous
  • Rosettes formed the first year and bolt early in May to June of the next year.


Habitat

  • Found in disturbed areas, such as overgrazed pastures, rangelands, roadsides and right-of-ways


Plant


Vegetation

  • Dark green with lighter, mid-rib
  • Hair on underside of leaves
  • Mature plants are 3 to 8 feet tall with flower heads at the tips of shoots
  • Spines along edges of stems and leaves
  • Stems are winged


Roots

  • Tap root


Flower

  • Bracts are narrow and tipped with a spine
  • Color: reddish-purple
  • One half to one inch wide
  • Second season: June to September


Seed

  • Lacks Pappus


Seedling

  • Seedlings spend their first growing season as rosettes


Reproduction

  • Seed


Control


Biological

  • Not allowed


Chemical


Cultural

  • Grass competition; promote grass growth with fertilization, irrigation and reseeding.
  • Prevention - maintain health of site
  • Removal - Must be repeated as new plants germinate
  • Re-vegetation of highly disturbed sites


Mechanical

  • Burning - N/A
  • Grazing - N/A
  • Mowing - Not effective alone


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