St John’s wort control

Access all the information needed for control of this noxious weed, including weed identification, herbicide application and spray timings.


St John’s wort description

St John’s wort identification

St John’s wort is a perennial herb that can grow up to 1 m tall. It has stemless small leaves dotted with clear oil glands that have a perforated appearance when held to light. Stems are reddish in colour.

Flowers have five yellow petals, three bunches of many stamens. St John’s wort is widespread in pastures, water catchment reserves, forests and national parks and can cause photosensitisation in livestock.

It infests large areas of New South Wales, Victoria and South Australia and is a serious weed on tablelands and slopes areas as it is most suited to areas receiving more than 600 mm annual rainfall at altitudes of 600 m to 1500 m.

St John’s wort control

Controlling St John’s wort

For control of St John’s wort, apply high-volume hand spraying of Grazon Extra at a rate of 500 mL/100 L of water applying 3000 L/ha to thoroughly wet the foliage of a dense infestation; lower spray volumes (2000 L/ha) will be effective on moderate to sparse infestations. Boom spraying with Starane Advanced at 1.8 L/ha and 200–250 L of water/ha is also effective and aerial application via helicopter using Grazon Extra at 4 L/ha is effective for hillside spraying.

Ensure the plant is actively growing (15–50 cm tall), and both the upper-flower canopy and sub-canopy lying prostrate are wet. Focus on spraying open areas where pasture productivity can be improved by the removal of St John’s wort without damaging remnant vegetation.

Herbicides for control of St John’s wort

Product#Method of applicationRate*State
Grazon® Extra Herbicide Foliar spray 500 mL/100 L of water All
Starane® Advanced Herbicide Foliar spray 300 mL/100 L of water All
Trezac® Arylex® active Herbicide Foliar spray 200 mL + 300 mL Starane® Advanced/100 L of water All
Grazon® Extra Herbicide Boom application 2 to 4 L/ha ACT, NSW
Starane® Advanced Herbicide Boom application 1.8 L/ha (200 L water/ha) All
Grazon® Extra Herbicide Controlled droplet application Apply undiluted All
Grazon® Extra Herbicide Gas gun application 500 mL/10 L of water ACT, NSW, Tas, Vic
Grazon® Extra Herbicide Aerial (helicopter only) 4 L/ha ACT, NSW

# Note: Preferred product option in bold.  * Consult label for details of growth stage and use, especially where range of rates is given.

Treatment timing

Timing for St John’s wort control

Spot spraying is best carried out when St John’s wort is in flower (Nov–Jan) because it can be easily seen then and is at its most sensitive period to herbicides. Spraying should begin six to eight weeks after substantial rain and when St John’s wort reaches the 50% yellow bud – 50% open flower stage.

Grazon® Extra Herbicide
Key: Best time to spray/treat Can spray/treat if conditions are suitable Do not spray/treat