Idaho OnePlan recommends the website of the
Idaho Weed Awareness
Campaign as the best resource for up-to-date information about
Idaho's noxious weeds, and their control.
Source for this page: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller
Musk thistle (Carduus nutans), 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.
Musk thistle is a biennialPlant that germinates in one growing season, then flowers, seeds, and dies during a second or winter annualPlant that germinates, flowers, seeds, and dies during one growing season that can grow up to 8 feet tall. Leaves are up to 10 inches long, dark green with a light green midribThe center and usually most prominent vein on a leaf, spiny, and deeply lobedA cut into a leaf from the edge toward the center; greater than toothed, but not quite compound. Solitary, lightly spiny, and noddingA flower that is not pointed upward, but bent downward or sidewise to the stem flower heads develop at the stem tips in midsummer and grow to a diameter of 1½ 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 hairlike plumeA hairlike or featherlike structure, often on a seed.
Musk thistle is widely though sparingly present in North America and is present in northern, central, and eastern Idaho counties..
Biological control agents (a seed head weevil and a rosette crown weevil) have provided good control of musk thistle. Herbicides offer effective control.