Blue Mountains National Resources Institute

Wanted: DEAD!

St. Johnswort

Alias: Klamathweed

• Stems: Often reddish. Woody at base. Main stem erect, single or several from the base of the plant, usually accompanied by many slender weak sterile basal stems. 1 to 3 feet tall.
• Leaves: Numerous, borne in pairs, if held to light appearing as if pinpricked and with tiny black dots on the margins.
• Flowers: 3/4-inch in diameter with numerous stamens, bright yellow, petals with black dots on margins, borne in clusters. Flowering period is during June and July.
• Fruits: Splitting at maturity into three segments. Gelatinous coating helps seeds stick to fur and clothing when wet. Seeds numerous, about 1/20-inch long, dark brown, microscopically pitted.

St. Johnswort is a perennial that propagates vegetatively by underground stems or runners. It is cumulatively poisonous to livestock. Light-pigmented animals develop blisters and scabs around the mouth, eyes, ears, nose, and feet, especially when exposed to sunlight. Dark-colored animals are less affected. It invades farm and pasture lands.

Control:

• Biological: Several beetles have been released with good success in controlling this weed. Klamathweed beetle has been working since 1948 in some heavily infested areas in Oregon. A root-boring beetle (Agrilus hyperici) has had success in Idaho and Washington. Climate is a limit on beetle populations.
• Mechanical: Repeated cultivation destroys the weed; it is not found in any cultivated crop. Mowing several times to prevent maturation also helps control the plant.
• Chemical: Selective herbicides are available, although restrictions may apply. Consult your Weed Board for more information.

Report all sightings to your local Weed Board