Weed Control
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St.Johns Wort
Information | Images
Hypericum perforatum
Perennial
Identification and management tips
- St. Johnswort flowers have five yellow petals. The leaves, when held up to the light, appear to have tiny, transparent perforations.
- St. Johnswort is a tap rooted perennial plant that spreads by seed and by underground and aboveground creeping stems.
- St. Johnswort flowers from June to September.
- A single plant is capable of producing 15,000 to 33,000 seeds per year. The seeds may remain viable in the soil for up to ten years.
- On small and isolated infestations, hand pulling or digging of young plants may be effective if repeated several times per season.
- St. Johnswort can be difficult to eradicate with herbicides because of its extensive root system, but control of new or small infestations can be accomplished.
- In pasture, rangeland, and non-cropland sites, foliar applications of 2,4-D at 2 quarts per acre will destroy the plant in seedling and pre-flowering stages. Spring application of one quart per acre of picloram is also effective and recommended.
Most effective control methods and timing
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Prevention (Prev)
Monitor and destroy new plants before seed production.
Mechanical (Mech)
Hand pulling, digging, cutting, mowing and tilling.
Cultural (Cult)
Biological control agents, livestock grazing, and revegetation practices.
Chemical (Chem)
Selective herbicides based on the plant and the specific location. Check our weed fact sheets for specific control information.
Links
- University of Nevada Cooperative Extension: Managing St. Johns wort
- USDA Forest Service: Invasive Plants Website: Weed of the Week St. Johns Wort
Photo credits
Left to right:
- Richard Old, XID Services, Inc., Bugwood.org