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Species
Information
- milk
thistle
- Silybum
marianum (L.) Gaertn.
- USDA
Symbol: SIMA3
- Oregon
Noxious Weed Designation: B
- Pictures
Identification:
Biennial or winter annual; blooms from April to July. Grows 2 to 6 ft tall. Stems stout, rigid and generally branching. Leaves broad, clasp stem, have spiny margins and have white marbling along veins. Flower heads reddish-purple and have leathery spine-tipped bracts.
Impacts:
Milk thistle is a native to the Mediterranean region of Europe. It infests roadsides, waste areas and grazing lands and often occurs in association with Italian and slender-flowered thistles. Once established, it forms dense clumps which exclude livestock and crowd out more desirable forage species. It has the potential to invade extensive acres of pasture land. Milk thistle seed is valued as an herbal medicine.
Biological
Controls: One approved biocontrol agent, a seed head weevil, has become established in Oregon; however, they do not always make their way to the seeds due the large receptacle on this plant.
Oregon
Maps of Milk Thistle Distribution
Links:
USDA
Plants Database information on milk thistle
GRIN
Database information on milk thistle
Oregon Department
of Agriculture information on milk
thistle
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