Stem

Up to 4 ft. tall with a woody base; highly branched; lacks hair (glabrous) and often rust colored with 2 ridges that run the length of the stem

Common St. Johnswort seedling

Leaves

Opposite, oval to strap-like (linear), prominent veins, less than 1 in. long, lack hair and no leaf stems (petioles); edges (margins) are smooth with the lower surface lined with small black dots
Surface covered with tiny transparent dots that can be seen by holding the leaf up to the light

Photo of fingers holding st. johnswort leaf

Common St. Johnswort leaf

Flower

0.75 in. diameter; 5 yellow petals that often have tiny black dots around the edges; many stamens; clustered at tips of branches

Common St. Johnswort flower

Root

Stout taproot with spreading rhizomes

Common St. Johnswort plant

Other

Grows best on coarse-textured, gravelly, well-drained soils; known to occur in Elko county
Perennial; reproduces by seed and rhizomes
Ingestion causes skin irritation and weight loss in white-haired animals; sometimes cultivated as a crop and used for medicinal purposes (as an antidepressant)
Also known as Klamath weed

Control

Mowing, grazing and burning are NOT effective
A biological control agent is available
Apply 2,4-D or glyphosate to actively growing plants prior to bloom; aminopyralid, metsulfuron or picloram pre or post-emergence

Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Nevada Noxious Weed Field Guide – Common St. Johnswort, Extension, University of Nevada, Reno, Field Guide

Extension Associated Contacts

Heidi Kratsch

Also of Interest:


Needs Assessment for Noxious Weeds in Churchill County: Part 4 of 5 - Criteria for Herbicide Use and Selection This fact sheet is the fourth in a series of five that reports the results of a needs assessment survey completed by faculty in University of Nevada Cooperative Extension (UNCE). The survey attempted to identify the major issues related to the management and control of weeds in N... Davison, J., Powell, P., Schultz, B., and Singletary, L. 2012, University of Nevada Cooperative Extension
Nevada’s Priority Agricultural Weeds: Hoary Cress Plants commonly referred to as hoary cress (Cardaria sp.), or short whitetop, are one of three different but closely related perennial forbs. The Cardaria species are widespread across all eleven Western states, including every county in Nevada. B. Schultz, S. Foster 2021, Extension, University of Nevada, Reno, SP-21-03
Nevada Noxious Weed Field Guide – African mustard African mustard is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., H. Kratsch, Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
Nevada Noxious Weed Field Guide – Common crupina Common crupina is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
Nevada Noxious Weed Field Guide – Crimson fountaingrass Crimson fountaingrass is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide

Associated Programs

Master Gardeners of Nevada

Program trains local gardeners to provide research-based horticulture information to Nevadans

Master Gardeners of Washoe County

Master Gardeners provide free, research-based horticulture information to Nevadans.

ladybug larva eating aphids on a pepper plant

Integrated Pest Management

Integrated Pest Management program is a long-term management strategy that uses a combination of tactics to reduce pests to tolerable levels with potentially lower costs for the pest manager and minimal effect on the environment.

Nevada Noxious Weed Field Guide – Common St. Johnswort