Scotch Thistle (State designated weed)

Scotch Thistle (State designated weed)

• Onopordum acanthium
• Asteraceae (Sunflower family)

Scotch thistle is a native of Europe and eastern Asia and is now sparsely naturalized over much of the U.S., found typically in waste areas and on roadsides. It is an aggressive plant that can form dense, impenetrable stands.

Growth Habit: Upright biennial, sometimes annual, up to 8 feet tall. Rosette formed first year, flowering stem elongates second year.

Leaves: Large, coarsely lobed, hairy on both sides, velvety gray appearance. Margins lined with sharp conspicuous spines. Basal leaves up to 2 feet long and 1 foot wide.

Stem: Upright, branching, spiny leaf wings extend down onto stem, covered with dense fine hairs.

Flowers: Solitary, terminal, 1 to 2 inches in diameter, violet to reddish colored. Bracts spine tipped. One plant can produce up to 40,000 seeds; reproduces by seed only.

Root: Large fleshy taproot.

Status: State Designated Noxious Weed, Category 2 Fremont County. Localized. No tolerance of new infestations and aggressive control on all known infestations.

Control: Chemical controls or mechanical removal (digging) can be effective. FCWP offers a 40 percent Cost Share on chemicals for controlling this species. Contact your local weed and pest office for further treatment recommendations.

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