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Noxious Weeds

Musk Thistle

Musk thistle was introduced to the U.S. in the early 1900s and is now widespread throughout North America. It is native to southern Europe and western Asia. It invades pasture, range and forest lands along with roadsides, waste areas, ditch banks, stream banks and grain fields and can grow under a wide range of environmental conditions.

Growth Habit: Musk thistle is a biennial or sometimes winter annual, with a rosette that forms the first year and a flowering stem that elongates up to 7 feet the second year.

Leaves: Dark green with light midrib, hairless on both sides, long sharp spines.

Flowers: Produces several solitary, terminal, nodding heads, 1½ to 3 inches in diameter, deep rose to violet to purple. Spreads by seed; can produce in excess of 20,000 seeds per plant. Unlike other thistles, the bract underneath the flower is papery rather than spiny.

Root: Fleshy taproot, hollow near ground surface.

Other: Musk thistle is not grazed by livestock or wildlife. Left untreated, it can produce an almost impenetrable infestation which crowds out other desirable plants.

Status: State Designated Noxious Weed, Category 3 Fremont County. Regional, no tolerance of further spread, control and management of current infestations and aggressive control in areas otherwise free of these weeds.

Control: Since herbicide is ineffective on the mature plant, it is important to spray the rosette stage or dig up the plant. Dig up most of the root and dispose of flower heads. Biological controls have been effective and are used in Fremont County. FCWP offers a 40 percent Cost Share on chemicals for controlling this species. Contact your local weed and pest office for further treatment recommendations.

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Collage clockwise from top: Steve Dewey, Utah State University; Dewey, USU; Loke T. Kok, Virginia Polytechnic Institute and State University

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