St. Johnswort, also called Klamath weed, is an erect, opposite-leaved perennial weed, ranging from two to four feet tall arising from a taproot. The plant can have single or multiple stems. The reddish stems are smooth, somewhat two-edged, woody at the base, and branching out toward the top of the plant. The narrow, lance shaped leaves are about one inch long, stalkless with pointed tips. Each leaf is spotted with tiny translucent dots. Each flower has five yellow petals and many yellow stamens. The black dots often visible along the petal margins are glands containing hypericin. This red pigment is also visible in glands on leaf margins giving the leaf a perforated look. The inflorescence is a flat topped cluster of many flowers found at branch ends. The extended flowering period is from May to late September. St. Johnswort spreads both by underground and above-ground creeping stems, and by seed.

St. Johnswort 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 and Management:
Wear gloves and avoid touching the eyes when collecting. Photosensitivity such second degree blisters could occur to the skin.

	Manual - Pull new or small infestation sites. Repeated pulls to remove the whole plant and lateral roots. Do not leave plants at the site, since vegetative growth will occur, and the seed source will remain. Regular tilling is effective where feasible.
	Chemical - It can be effectively controlled using any of several readily available general use herbicides such as 2,4-D right after germination on new seedlings and before blossoms open. Repeated applications will be necessary. Follow label and state requirements.
	Biocontrol - Two foliage beetles, Chrysolina hyperici and C. quadrigemina were released in California from 1945 to 1946, and established within two years. A root-boring beetle Agrilus hyperici and a leaf bud gall-forming midge Zeuxidiplosis giardi were released in 1950 to help the Chrysolina spp. These established California colonies became the source for collections and distribution to Hypericum perforatum infestations throughout the western United States. Recently released and established is the moth Aplocera plagiata.

Biological controls: Several insects have been introduced to dampen the spread of St. Johnswort, including a moth that eats foliage and flowers (Aplocera plagiata), a root-boring beetle (Agrilus hyperici), a midge which forms galls in the leaf buds (Zeuxidiplosis giardi), and foliage feeding beetles (Chrysolina hyperici & C. quadrigemina). Insect control with this latter beetle has proved very effective at the National Bison Range near Moiese, Montana, with moderate control every fifth year and major control every tenth year. The beetle population builds up over time, until the insects consume all new growth on the plants and eventually devour the stems. There were 8,000 acres of Saint Johnswort on the Bison Range in 1994, but only 400 acres by 1997. This biocontrol project saved an estimated $400,000 compared to herbicide applications.