Abstract

Common St. Johnswort is a perennial weed accidentally and intentionally introduced to North America from Europe. It is a member of the Clusiaceae family and also bares the common names St. John’s wort, goatweed, and Klamath weed. Common St. Johnswort is perennial, relatively long-lived, and reproduces by short rhizomes that initiate from the stem base and by seed. Seeds can survive in the soil for ten years.

Herbarium records indicate that populations of common St. Johnswort in Montana were first reported from Gallatin County in 1905 and as of 2007 have been reported from 26 of Montana’s 56 counties infesting an estimated 68,065 acres. It is recognized as an economically important pest in temperate regions world wide and has a long and storied history as a medicinal plant. It invades foothill rangeland, pastures, and open forest sites where it reduces available forage to livestock and wildlife and poses a threat of poisoning. It also occurs in riparian areas, along roadsides, and along railroad rights-of-way.

Common St. Johnswort can be controlled using picloram (one to two quarts Tordon^® per acre) or metsulfuron (one ounce Escort^® or Cimarron^® per acre) applied to actively growing plants before bloom. Grazing management of common St. Johnswort with all species of livestock is risky because it contains hypericin which causes blistering of skin of grazing animals that consume it and are exposed to the sun. In extreme cases, affected parts of the mouth may prevent animals from drinking and foraging. Five insects are available for biological control of common St. Johnswort. The release of two foliar feeding beetles in 1945 and 1946, Chrysolina hyperici and C. quadrigemina, were the first attempt at biological control using insects in the United States and were very successful in reducing St. Johnswort populations in California.

Figure 1. Common St. Johnswort flowers bloom around mid-summer.

< Back to Ecology and Management of Common St. Johnswort

Last Modified: 07/27/2007