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plumeless thistle (Carduus acanthoides)
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ODA rating: A and T
 
USDA Symbol: CAAC
Oregon plumless thistle distribution
 
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Images courtesy of Dan Sharratt, Oregon Dept. of Agriculture

If images are downloaded and used from the ODA web site please be sure to credit the photographer.
 
 
Description
Winter annual or biennial herb; flowers May to July. Grows 1 to 4 feet tall. Stems covered with spiny wings. Rosette leaves 4 to 8 inches long, stem leaves alternate and blend into the stem. Flower heads in clusters of 2 to 5 and usually purple but can be yellow or white.
 
Impacts
Each plant generates thousands of seeds. It is very aggresive, limiting grazing and other livestock management, threaten forage production and restrict recreational activities.  Plumeless thistle invades pastures, valleys, fields, roadsides and open native habitats.
 
Distribution in Oregon


Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. This weed is being managed for eradication or containment. There are two approved biocontrol agents for use in other states: a seed head weevil and a crown weevil.
 
Informational links
Printable trifold plumeless thistle brochure (pdf 512KB)