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Musk Thistle Asteraceae (= Compositae), the aster family
BACKGROUND: Musk thistle, a native of Eurasia, was probably introduced into the U.S. as an ornamental in the early 20th century. It spreads by seeds, often forming nearly impenetrable stands. It can grow under a wide range of environmental conditions.
DESCRIPTION: Musk thistle is a biennial or winter annual that can grow up to 8 feet tall. Leaves are up to 10 inches long, dark green with a light green midrib, and spiny and deeply lobed. Solitary, lightly spiny, and nodding flower heads develop at the stem tips in midsummer, and grow to a diameter of 11/2 to 3 inches. Blossoms are deep rose to violet or sometimes white in color. Seeds are 3/16 inch long, shiny, yellowish brown, and have a hair-like plume.

DISTRIBUTION: Musk thistle is widely though sparingly present in North America and is present in northern, central, and eastern Idaho counties.
CONTROL: Biological control agents (a seed head weevil and a rosette
crown weevil) have provided good control of musk thistle.
Herbicides offer effective control.