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musk thistle (Cardus nutans)
ODA rating: B
 
USDA Symbol: CANU4
Oregon musk thistle distribution

Other common names
nodding thistle

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musk thistle flower
Image courtesy of Eric Coombs, Oregon Dept. of Agriculture
musk thistle plant
Image courtesy of Eric Coombs, Oregon Dept. of Agriculture
musk thistle infestation
Image courtesy of Shannon Brubaker, Oregon Dept. of Agriculture
 
If images are downloaded and used from the ODA web site please be sure to credit the photographer.

Description
Biennial; blooms in early June. Grows three to six feet tall. Flower heads large, purple, solitary and usually nodding. Musk thistle has dark green leaves with light green midrib and wavy, spiny lobed margins. Leaves have a smooth waxy surface and appear winged at attachment to stem.
 
Impacts
Musk thistle is unpalatable to wildlife and livestock hence selective grazing leads to severe degradation of native meadows and grasslands as wildlife focus their foraging on native plants, giving musk thistle a competitive edge. It is thought to produce chemicals that hinder the growth of other plants. The spines can be harmful to animals and can hinder their movement through infested areas. Found in pasture, range and timberlands, it spreads by seeds, taking advantage of human disturbance. Prolific in moist condition. Commonly infests ditch banks, roadsides, and cereal fields.
 
Introduction
Musk thistle is native to southern Europe and western Asia. Introduced in ship’s ballast in the eastern United States in the mid 1800s. First recorded in Pennsylvania in 1852.
 
Distribution in Oregon
Klamath County is the most heavily infested musk thistle county in Oregon. The first record of milk thistle in Oregon is 1922 in Multnomah.

Biological controls
Six biocontrol agents have been approved for release. Three of these, a crown weevil, a seed head weevil and a flower fly, have been established in Oregon.
Cheilosia corydon
Rhinocyllus conicus
Trichosirocalus horridus
Urophora solstitialis