Canada Thistle
(Cirsium arvense L.)
Sunflower family- Asteraceae

Photo by Tom Whitson, Roy Reichenbach

Produced by Wyoming Weed & Pest Council in cooperation with Sandoz Crop Protection Corp.

Growth Habit: Perennial, erect, up to 4ft. tall.

Leaves: Varies from light to dark green, oblong or lance shaped, deeply cut, spiny toothed margins (some may be smooth) slightly hairy below. Tremendous leaf variablity.

Stem: Smooth to slightly hairy, branched at the top.

Flower: Small bristly clusters, 3/8 to 5/8 inch in diameter, light lavender to deep rose purple. Plants are male or female. 

Roots: Extensive, fleshy, creeping rootstocks.

Seeds: Smooth, light to dark brown, tipped by a cupped conical point, approx. 1/8" long. 

Reproduction: by seed and creeping rootstocks.

Habitat: cultivated fields, pastures, rangelands, forests, along roadsides, ditches & riverbanks. 

Biological Controls: Canada Thistle stem weevil (Ceutohynchus litura), Thistle stem gall fly (Urophora cardui), Thistle head weevil (Rhinocyllus conicus). 

Herbicides:Tordon & 24D, Curtail, Escort, Milestone