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  • Lander Office 307-332-1052
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  • fcwp@wyoming.com

Common St. Johnswort (State designated weed)

Originally from Europe, common St. Johnswort is a plant common to the Pacific coast but it is also present in Wyoming.

Growth Habit: Upright flowering perennial, reproducing by seeds or short runners.

Leaves: Up to an inch long, the leaves are generally bright green and grow directly from the stem having no leaf stalk; oval with smooth edges, grow opposite on the stem and are covered with transparent dots.

Stems: About 1 to 3 feet high, erect, with numerous branches, somewhat two-ridged, rust-colored, woody at their base.

Flowers: Numerous yellow flowers, stamens stand up from the petals almost as big as the leaves; five petal flowers often have tiny black dots on the petal edges and produce ¼ inch long, rust colored, three chambered, seed pods, each containing numerous seeds.

Roots: Perennial with many upright branching stems and short runners.

Other: Known for its medicinal uses; crowds out native forage and is toxic to livestock.

Status: Status: State Designated Noxious Weed, Category 1 Fremont County. No known infestations in Fremont County. No tolerance, with a goal of early detection and eradication. Call FCWP if this weed is detected.

Control: Chemical controls can be effective. FCWP offers a 40 percent Cost Share on chemicals for controlling this species. Contact your local weed and pest office for further treatment recommendations.

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Norman E. Rees, USDA Agricultural Research Service, Bugwood.org

Norman E. Rees, USDA Agricultural Research Service, Bugwood.org