The Mission of the Yellowstone County Weed Department is to assist the public, private, and other government agencies to manage and control existing noxious weed infestations as well as to prevent new invasive species from infesting Yellowstone County.

Canada ThistleCirsium arvense L.

Sunflower family- Asteraceae

Photo from Montana Weed Control Association

Stem

Rosette

Leaf

Bloom

Mature

Dormant

Photos from Montana Weed Control Association

Video Supplied By Ravalli County Weed District

Attribute	Description
Growth Habit	Perennial, erect, up to 4 ft. 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 variability.
Stem	Smooth to slightly hairy, branched at the top.
Flower	Small bristly clusters, 3/8 to 5/8 in. 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 & 2,4-D, Curtail, Escort, Milestone.