 |
| OSU HOME | EXTENSION HOME | ONLINE CATALOG | ORDERING INFORMATION |
| Extension Service |
|
A Pacific Northwest Extension Publication St. JohnswortPNW 442Reprinted March 1999 J.P. Fitzsimmons and L.C. Burrill Do you want to print a copy? We recommend downloading the print version (32 K). First download the free Adobe Reader, if you don't already have it. Contents Identification Control St. Johnswort (Hypericum perforatum), also called Klamath weed and goatweed, was introduced from Europe and was found in California about 1900. It was a major pasture weed west of the Cascade mountains from Tacoma south to central California until the successful introduction of the chrysolina beetle, a leaf-eating insect. East of the Cascades, St. Johnswort established and spread rapidly, invading pastures, non-crop areas, and grazeable woodlands. It seems to grow best in sandy, gravelly soils but commonly is found in heavy soils. When livestock eat St. Johnswort, they become sensitive to sunlight. Light-colored animals are most susceptible, developing dermatitis, including skin blisters and hair loss. Symptoms do not result from casual contact; the plant must be eaten. Animals avoid eating St. Johnswort when possible, so the displacement of desirable forage probably is a greater concern. St. Johnswort in hay retains the harmful chemicals, and animals have trouble avoiding it. Livestock prefer grass over St. Johnswort when both plants are present. This may lead to overgrazing of grass and more opportunity for the weed to spread. St. Johnswort commonly is found in ornamental plantings, Christmas tree plantations, orchards, roadsides, and other sites where ground is not tilled every year. St. Johnswort is a Class C noxious weed in Washington and a Class B noxious weed in Oregon. IdentificationSt. Johnswort is in the St. Johnswort family with the old Latin name Guttiferae and the new name Hypericaceae. It is a perennial plant that spreads by seed and by underground and above-ground creeping stems. Main stems are reddish and woody at the base. Plants grow from 12 to 36 inches tall with numerous upright stems from the base of the plant. Multiple branching occurs above a short, leafy, often prostrate stem area. Leaves are numerous, simple, opposite, and borne on the stem with no petiole; they occur the length of the stem. When held up to the light, each leaf appears to be perforated by pin pricks, hence the name "perforatum." Flowers are numerous in flat groups at the top of the plant. Each flower contains five deep-yellow petals with minute, black dots along the margins and has many stamens. Fruits are three-cell capsules with numerous seeds that are 1/32 inch long, pointed at both ends, glossy, and dark brown. Seeds have a gelatinous coating that sticks to legs, hooves, boots, vehicles, and other objects when the seeds are wet. Later in the day, after the dew evaporates, the seeds fall back to the ground. Seeds are widely distributed this way.
ControlBiological. Several insects have been tested and released in the Pacific Northwest to control St. Johnswort. The Klamath weed beetle (Chrysolina quadrigemina) was released in the Pacific Northwest in 1948 with great success in some heavily infested areas. Another beetle, Chrysolina hyperici, also was released and is better adapted to wetter sites. A root-boring beetle, Agrilus hyperici, was introduced and has become established in eastern Washington and northern Idaho. Attempts to establish a seed head fly, Zeuxidiplosis giardi, failed. A defoliating moth, Aplocera plagiata, is established in a few sites in northern Washington. The cyclic increase and decrease of the St. Johnswort population over years is a normal response to a change in the population of the biocontrol agents. In northeastern Washington, the beetles control St. Johnswort less effectively because climate limits their populations. Mechanical. Repeated cultivation soon destroys this weed; therefore, it is not found in cultivated crops. Rotation of pastures or perennial plantings to cultivated crops for 1 or 2 years reduces problems. Mowing several times to prevent seed maturation helps control spread of the plant. Chemical. Selective herbicides are available for control of St. Johnswort in grass pastures. Grazing restrictions may apply, so follow label recommendations carefully. Several applications may be necessary to control the weed. Selective control is more difficult in grass-legume pastures. Spot spraying or sponge wipers may be used. Herbicide registrations change frequently; therefore, this publication does not contain specific herbicide use instructions. Registered uses are summarized each year in the Pacific Northwest Weed Control Handbook. In addition, detailed instructions for herbicide use are provided on herbicide container labels and in other literature provided by herbicide manufacturers. Prepared by Jim P. Fitzsimmons graduate student, crop and soil sciences; and Larry C. Burril, Extension weed specialist, Oregon State University. Reprinted March 1999 |
|
Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the Oregon State University Extension Service, Washington State University Extension, University of Idaho Cooperative Extension System, and the U.S. Department of Agriculture cooperating. The three participating Extension Services offer educational programs, activities, and materials--without regard to race, color, religion, sex, sexual orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era veteran status--as required by Title VI of the Civil Rights Act of 1964, Title IX of the Education Amendments of 1972, and Section 504 of the Rehabilitation Act of 1973. The Oregon State University Extension Service, Washington State University Extension, and University of Idaho Extension are Equal Opportunity Employers. Copyright © 1995- Oregon State University. Disclaimer. |