St. John's Wort - Hypericum perforatum

Description: St-John’s-Wort belongs to the Clusiaceae family and grows .01 to 1.0 m tall. It has numerous bright yellow flowers, 2 cm in diameter that occurs in flat-topped clusters. Flowers have 5 separate petals that are 2 times as long as the septal. The leaves are opposite, oval-shaped, with prominent veins, 1-3 cm. long and covered with transparent dots. The stems are erect, 2-sided, rust coloured, and have numerous branches (Ministry of Agriculture, Lands and Fisheries, 2002). This plant is native to Europe but arrived in North America in the late 1700s and become an established weed in BC in the 1940s (White et al 1993).

Type: perennial forb

Habitat and Impacts: St-John’s-Wort invades grazed and disturbed lands along roadsides and grows in low to mid-elevations in coastal, grassland and open forested regions. It can displace native plant species and reduce livestock and wildlife forage. (Ministry of Agriculture, Lands, and Fisheries, 2002). The plant contains a phototoxin which can cause skin irritation to livestock with light coloured skin when exposed to sunlight. It is generally not palatable to cattle (Majak et al 2008) St- John’s Wort is also known to be a skin irritant for humans.

Method of Spread: St. John’s-Wort reproduces by seed and vegetatively from the roots. The rhizome root system spreads laterally and is capable of forming new buds that separate from the parent. Each plant produces approximately 15,000- 30,000 seeds. The seeds have a gelatinous coat that allows long-distance dispersal and can remain viable in the soil for 6-10 years. (Ministry of Agriculture, Lands, and Fisheries, 2002).

Location: St. John’s-Wort is not well established in the Cariboo Chilcotin Coast Region. Most infestations have been located in the Bella Coola area and Tweedsmuir Park; however, a few sites have been located in the Quesnel area.

Management Options:

Mechanical: Can be managed by tillage in agricultural fields.

Chemical: Combinations of 2,4-D and picloram, or 2,4-D and glyphosate have been successful in managing this weed in the US (Ministry of Agriculture, Food and Fisheries, 2002).

Biological: Several biocontrol agents are available for St. John’s-Wort including Agrilus hyperici (root feeding beetle), Aphis chloris (sap sucking aphid), Aplocera plagiata (foliar feeding moth), Chrysolina hyperici (foliar feeding beetle), Chrysolina quadrigemina (foliar feeding beetle), Chrysolina varians (foliar feeding beetle). Chrysolina hyperici and Chrysolina quadrigemina have been successful in the Kootenay region of BC but none of these agents have been tested in the CCCIPC region (Ministry of Forests and Range, 2007).

CCCIPC Priority and Treatment Strategy: Priority4 (Biological Control)

Treatment Options:

Local Level – Chemical control and tillage for agricultural sites.
Landscape Level - Biological control for larger infestations.

Richard Old, Xid Services, Inc.

St. John's Wort Plant

British Columbia Minsitry of Forest and Range

St. John's Wort biocontrol foliar feeding moth

St. John's Wort flower


Invasive species profile taken from the Cariboo Chilcotin Coast Invasive Plant Committee Invasive Plant Regional Strategic Plan

Page last modified: October 30, 2018 09:44:02 PDT