Plumeless Thistle

Plumeless Thistle

Carduus acanthoides

Colorado List B - Eradication required in Jefferson County

Information Sheet (pdf)

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

• View Information Sheet (PDF)

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.