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Species
Information
- Canada
thistle
- Cirsium
arvense (L.) Scop.
- USDA
Symbol: CIAR4
- Oregon
Noxious Weed Designation: B
- Pictures
Identification:
Perennial; blooms midsummer. Leaves wavy margined to lobed, up to 6 in long and armed with yellowish spines. Small purple to white flowers in clusters. Extensive deep seated root system spreading horizontally. Large seed production but low percentage of viable seeds.
Impacts: Canada thistle can be found growing practically anywhere from the coast to the desert. A lack of control in vegetable crops and pastures will result in a reduction in crop yield and quality. New infestations can originate from windborn seeds, but in cultivated crops are more often caused by redistribution of root fragments by tillage practices.
Biological
Controls: Four approved biocontrol agents, a stem weevil, a seed head weevil, a crown weevil, and a stem gall fly are established in Oregon.
Oregon
Maps of Canada Thistle Distribution
Links:
USDA
Plants Database information on Canada thistle
GRIN
Database information on Canada thistle
Oregon Department
of Agriculture information on Canada thistle
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