Italian Thistle
Carduus pycnocephalus
Washington State Classification
Class A — Eradication Required Statewide
Italian thistle invades pastures and rangeland.
Quick Reference
Identification
Growth Habit
Italian thistle is a spiny annual or sometimes biennial that can grow 6 to 8 feet in height.
Leaves
Leaves green and nearly hairless above and have cobwebby hairs below. Leaves are pinnately lobed into spiny-lobed segments, with the terminal spine being most prominent.
Flowers
Flowerheads narrow and in terminal clusters of 1 to 5. Bracts at the base of flowerheads are stiff and upright with forward pointing hairs. Flowers are purple.
Fruit & Seeds
Seeds are light brown to brown with veins, 0.18 to 0.24 inches (4 to 6 mm long), with hairs attache at one end.
Impact
Italian thistle invades pastures and rangeland. It crowds out more desirable forage, as well as native plants, and excludes livestock grazing where infestations are dense.
Ecology & Spread
Habitat
Italian thistle grows in dry, open area such as pastures, rangeland, right-of-ways, and waste areas. Please click here to see a county level distribution map of Italian thistle in Washington.
Spread Mechanisms
Reproduction
Italian thistle reproduces by seed.
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Control Methods
Biological Control
- Two fungi have been evaluated as agents on Italian thistle. More information can be found by downloading our Written Findings.