By East Kootenay Invasive Species Council

St. John’s-Wort is a perennial invasive plant that was introduced as an ornamental and medicinal herb from its native range of Europe, Asia and North Africa. It grows in dense patches which can crowd out natural plants and reduce the grasses that animals feed on. Common St. John’s-Wort spreads by lateral roots and can produce up to 100,000 seeds per plant. St. John’s wort contains a poison that can cause light-coloured farm animals that eat it to have skin burns or blisters when exposed to sunlight.

How to Identify:

Common St. John’s wort grows from 0.3–1 m in height.

It has dark green, opposite leaves which show tiny transparent dots when held up to the light.

Flowers are bright yellow, with 5 petals each, and grow in clusters at the top of branches. It turns a rusty red colour after finishing flowering late in the summer and autumn.

Impacts:

St. John’s-wort invades grazed and disturbed lands. In dense stands, it displaces native plant species and reduces livestock and wildlife forage. The plant also contains a toxin that causes skin irritation and blistering in light-coloured livestock when they are exposed to sunlight.

Management Strategies:

Biocontrol: Several beetles (Chrysolina hyperici, C. quadrigemina, Agrilus hyperici), a moth (Aplocera plagiata), and an aphid (Aphis chloris) have been released in the province. Beetle populations are sustainable but require periodic relocation.

Mechanical: Tillage in agricultural fields helps control spread. Hand pulling before seeding and removing roots can prevent regrowth.

Herbicides: Several herbicides with the following active ingredients can control St. John’s Wort: glyphosate, 2,4-D, aminopyralid, picloram, and metsulfuron (read and follow the label instructions).

Cultural/Preventive: Promote diverse plant communities with perennial grasses and forbs.

Learn more here.

East Kootenay Invasive Species Council photos

The East Kootenay Invasive Species Council works to minimize the threat of invasive species that impact the environment, the economy and human health in the East Kootenay region of B.C., and we couldn’t do it without you! as a non-profit, we rely on grant funding and the generous support of our community to operate. Your donation will help us continue to protect the East Kootenay from invasive species. Donate here.

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