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
Photo of st. Johnswort plantCommon 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
Photo of common St. Johnswort flower
Common St. Johnswort flower

Root

  • Stout taproot with spreading rhizomes
Photo of common St. Johnswort plant
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
photo of common st. johnswort plant
 

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

Learn more about the author(s)

Heidi Kratsch
Heidi Kratsch
 

Also of Interest:

 
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 Davison, J., Powell, P., Schultz, B., and Singletary, L. 2012, University of Nevada Cooperative Extension
Nevada’s Priority Agricultural Weeds: Hoary Cress
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 Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
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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

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Master Gardeners of Nevada

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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.