Posted on 09.27.21 by Harney SWCD

Scotch Thistle, or Onopordium Acanthium

This invader is a biennial plant in the Asteraceae family that is native to the Mediterranean region. It spends its first year building photo-synthetic broad spiked leaves and a strong root structure. Once it begins upward growth, Scotch Thistle can reach 3-6 feet. Flower heads are 2 inches in diameter with a purple broad-brush shape.

Scotch Thistle has infested all Idaho counties and is found west of the Oregon Cascades. It loves dry pasture, fields, and disturbed sites.  As with many invasives, it is responsible for lost wildlife habitats and recreation areas.  Access to trails, stream banks,and fishing areas can be completely cut off by the spread of scotch thistle.

Seed from this plant are highly palatable to small birds, which causes a wide dispersal and rapid spread.

To treat, cut the rosette up and the plant will die. Herbicide like Milestone will kill the plant.  Cattle can be trained to eat scotch thistle.