St John's Wort Control Guide

St John's Wort 


  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see Herbicides for St John's Wort Control for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Revisit and regularly inspect the site and ensure follow-up is undertaken;
  • Use a combination of different control methods; and
  • Establish vigorous pasture (or native species) after removal to reduce re-infestation.


  • Don't introduce St John's wort to St John's wort-free areas (e.g. by failing to wash down machinery and equipment between sites);
  • Don't start your control program without first planning your approach;
  • Don't allow St John's wort to flower and set seed before treatment;
  • Don't rely on one attempt at removal - follow-up is essential;
  • Don't rely on just one control method.

Spread of St John's wort

  • St John's wort spreads by seed and by vegetative means (crown and rhizomes).
  • Seed is the main means of spread. A mature plant can produce between 15,000 and 30,000 seeds. St John's wort seed may remain viable for at least up to 20 years.
  • Seed is spread by wind, in water and soil, and as a contaminant of agricultural produce. The sticky capsule attaches to animal wool and fur, clothing and can also survive the digestive systems of most stock.
  • Cultivation, earthworks and roadside machinery can spread pieces of the crown or rhizomes to clean areas where the fragments produce new plants.

Avoid the introduction of St John's wort

  • Preventing the introduction of St John's wort to clean areas is the best means of control. Good hygiene practices are vital.
  • St John's wort is easy to identify when in flower, and small isolated infestations should be removed as soon as possible, preventing further spread.
  • See the Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading St John's wort.

Physical removal

  • Isolated plants and small infestations can be removed by hand, preferably before seeding.
  • Remove as much of the root system as possible as St John's wort can sucker from roots left in the ground.
  • Follow-up will be required to deal with any further germination or suckering.


  • St John's wort can be set back by cultivation which exposes and dries out the roots, then sowing to pasture.
  • The developing pasture should be left un-grazed for the first year to allow the subterranean clover maximum chance to smother the St John's wort.
  • Over-grazing will favour the weed as it reduces the competition from the pasture plants.
  • Grazing programs need to be well planned and carefully managed to ensure stock do not suffer poisoning.


  • Burning should not be used to control St John's wort. Burning stimulates reshooting and suckering and can worsen an infestation.

Chemical control

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