Cirsium arvense (L.) Scop.

Canada Thistle

Identification

Canada Thistle

Cirsium arvense (L.) Scop.

Life cycle: Perennial
Height: Up to 4 ft

Canada thistle is an erect perennial growing up to 4 feet tall. Leaves are variable shades of green, oblong or lance shaped, deeply cut, usually spiny with toothed margins and slightly hairy below. Stems are smooth to lightly hairy and branched at the top.

Flowers are about half an inch across, in small clusters, and light lavender to rose purple. Plants can be male or female. Roots are extensive and fleshy, and they are the major source of expansion. Seeds are smooth, various shades of brown and tipped by a cupped conical point, about an eighth of an inch long.

Control

Controlling canada thistle

Best timing: Treat at the early bud stage in early summer, or spray fall rosettes in late September or early October. Plan on two to three years of follow up.
Mowing and pulling: After harvest, cultivate before plants reach 3 inches tall and repeat until freeze up. Repeated mowing at the early bud stage helps, especially with herbicide.
Herbicide: On noncropland: clopyralid, picloram (Tordon), dicamba, Overdrive, aminocyclopyrachlor (Method) and aminopyralid (Milestone). In glyphosate resistant crops, glyphosate will not kill an established stand.
Biological control: Options are limited. The weevil and gall fly released for it have had little effect.

Always follow the product label, and check rates in the North Dakota Weed Control Guide from NDSU. Your county weed control officer can tell you what fits your land. Source: NDSU Extension W1411 (December 2025).

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