Plumeless Thistle

plumeless thistle habit
plumeless thistle rosette
plumeless-thistle-flower

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.

Treatment Timeline


JanFebMarAprMayJuneJulyAugSeptOctNovDec
Control











Removal











Herbicide











Growth











Rosette











Vegetative











Flowering











Seed