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

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  

Authors of this scholarly work are no longer available.

Please contact Extension's Communication Team for assistance.

 

Also of Interest:

 
Mineral County Needs Assessment: Community Needs and Issues
This fact sheet reports on community needs and issues through detailed tables of the top five community needs and issues with percentages of 207 households. Learn about the quality of life in Mineral County and both most and least important needs and issues.
 Emm, S. 2004, Extension | University of Nevada, Reno, FS-04-50
Community Needs and Quality of Life in Lyon County: Results of a Community Situational Analysis
This factsheet contains information on Lycon County's community needs and the quality of life. This was done by an analysis of respondents' answers to 21 questions about community needs that reflect the quality of life in Lyon County.
 Singletary, L. 2005, Extension | University of Nevada, Reno, FS-05-13