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Species
Information
- St.
Johnswort
- Hypericum
perforatum (L.)
- USDA
Symbol: HYPE
- Oregon
Noxious Weed Designation: B
- Pictures
Identification: Perennial; blooms June to July. Grows 1 to 3 ft tall. Stems erect, numerous branched, somewhat 2 ridged, rust-colored and woody at their base. Leaves opposite, oblong, not over 1 in long and covered in transparent dots. Flowers 3/4 in in diameter, bright yellow, numerous in flat-topped cymes with five petals with occasional small black dots around the edges. Stamens numerous, arranged in three groups.
Impacts: This difficult to control pest is found throughout most of the western U.S. It invades pasture and rangeland and is poisonous to livestock. Livestock seldom eat the plant unless pasture is scarce. The plant contains a toxic compound that causes photo-sensitivity; poisoning appears to be cumulative. Light pigmented animals develop blisters and scabs on the mouth eyes, ears, nose and feet, especially when exposed to sunlight. Dark colored animals are generally less susceptible.
Biological
Controls: There are five biological control agents approved for use on this plant. Four of these, three beetles and a moth, have been successfully established in Oregon. Currently the biological agents are not effective above the 2500 foot level.
Oregon
Maps of St. Johnswort Distribution
Links:
USDA
Plants Database information on St. Johnswort
GRIN
Database information on St. Johnswort
Oregon Department
of Agriculture information on St. Johnswort
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