St John's wort

General description

Erect perennial herb < 1.2 m tall. Rhizomes are slender and creeping. Stems are woody near the base, many-branched and have 2 longitudinal ridges. Leaves are opposite, stalkless and have translucent and occasionally black dots. Flowers are yellow with small black dots on the edges and are borne in terminal clusters in December – March. Fruit is a sticky capsule containing many pitted seeds and is green when young, ripening to brown.

What you need to know

Although St John’s wort is not a legally declared pest plant, it may still be invasive in some situations. Consider lower risk alternatives for your garden, such as native plants.

Habitats

Open areas, forest, riparian margins, grasslands, pasture, plantations, wasteland, roadsides.

Dispersal

Seeds dispersed by wind, water and animals. Vegetative spread from rhizomes. Human-mediated dispersal through dumping of garden waste, deliberate plantings and movement of contaminated soil, machinery and produce.

Impact on environment

Can displace native vegetation. Toxic to livestock.

Control

Site Management

Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Recommended approaches

Physical control

Method: Dig or pull out.

Plant parts requiring disposal: All parts.

Disposal options: Remove to greenwaste or landfill

Biocontrol

Check for the presence of agents: St John's wort beetles (Chrysolina hyperici and Chrysolina quadrigemina).

For more information about how biocontrol works, see What is biocontrol?

Community agrichemical control recommendations

Basic Growsafe certified: Foliar spray with 200ml glyphosate green per 10L of water.

Certified Handler/Experienced agrichemical user: Foliar spray with 200ml glyphosate green per 10L of water and 20ml penetrant.