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Scotch thistle (Onopordum acanthium)
ODA rating: B
 
USDA Symbol: ONAC
Oregon Scotch thistle distribution
 
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Image courtesy of Eric Coombs, Oregon Dept. of Agriculture. 
  Image courtesy of Dan Sharratt, Oregon Dept. of Agriculture. 
  Image courtesy of Bonnie Rasmussen, Oregon Dept. of Agriculture. 
 
If images are downloaded and used from the ODA web site please be sure to credit the photographer.
 
Description
Biennial that sometimes acts like an annual; blooms May-June. Often producees a rosette the first year but when acting annual it can grow 2-4 feet the first year and is capable of heights over 10 feet in the second. Large amount of soft white hair on upper leaf surface. Towering height, depending on available moisture. Winged tissue along stem. Purple flower. Stands dense and practically impenetrable because of spiny nature and large size. Spreads by seed.
 
Impacts
Scotch thistle is a wasteland weed that generally inhabits moist sites or drainages in dry locations. If not controlled, it presses into farmland or forms dense canopies in any area overgrazed or not under intense cultivation. It is a major issue in rangeland management in northeastern Oregon.
 
Introduction
Scotch thistle is a native of Asia and Europe but is now found throughout North America.
 
Distribution in Oregon
The first documented site in Oregon was 1892 in Benton County.

Biological controls
No approved biological control agent is available.