Square-Stemmed St John's Wort

(Hypericum tetrapterum)

Square stemmed St Johns wort, photo: John Crellin

What is square-stemmed St John's wort?

  • Square-stemmed St John's wort has the potential to become a significant riparian (river-side) weed in Tasmania.
  • Square-stemmed St John's wort is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of square-stemmed St John's wort are prohibited in Tasmania.

How to identify square-stemmed St John's wort

  • Square-stemmed St John's wort is an erect perennial (long-lived) herb growing to 1 metre high. Square-stemmed St John's wort is similar to St John's wort, however the reddish stems are almost square in cross-section.
  • The leaves are stem-clasping at the base and have numerous small oil glands that give the leaf a perforated appearance when held up to the light. The flowers are bright yellow with black glands dotted along the margins of the petals, and grow in small dense clusters at the end of the branches. The fruit is a sticky capsule containing numerous, light brown cylindrical seeds.
  • Germination occurs mainly in autumn after rain. Flowering occurs from spring through summer. The woody stems die back after flowering but may remain standing for months to years.
  • The rootstock or woody crown produces numerous horizontal rhizomes (underground stems) just below the surface; these rhizomes produce buds from which new above-ground growths develop each year in spring.
Square stemmed St Johns wort, photo: John Crellin
Images: Square-stemmed St John's wort plant & flowers, © John Crellin.

Square-stemmed St John's wort in Tasmania

  • Square-stemmed St John's wort occurs at several locations in the Huon Valley in southern Tasmania. All populations are relatively small.
  • Square-stemmed St John's wort occurs adjacent to streams and swamps from where it encroaches into moist pastures and riparian (river-side) vegetation. Square-stemmed St John's wort forms very dense stands and appears to be as strongly competitive as St John's wort.

What is the legal status of square-stemmed St John's wort in your area?

What you need to do

If you locate square-stemmed St John's wort anywhere in Tasmania, or if you find a plant that you think could be square-stemmed St John's wort, immediately contact Biosecurity Tasmania on 03 6165 3777 to report this weed.

Detailed management and control guidelines for square-stemmed St John's wort can be found in the Square-Stemmed St John's Wort Control Guide. Refer also to Herbicides for Square-Stemmed St John's Wort Control. For further information see DPIPWE's Weed Links and Resources.

See also
Herbicides for Square-Stemmed St John's Wort Control
Statutory Management Plan for Square-Stemmed St John's Wort
Weed Links and Resources

Other useful links
Pest Genie
APVMA

Square-Stemmed St John's Wort Control Guide

Do

  • 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;
  • 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

  • Don't introduce square-stemmed St John's wort to square-stemmed St John's wort to-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 square-stemmed St John's wort to 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 square-stemmed St John's wort

  • Square-stemmed St John's wort spreads by seed and by vegetative means (crown and rhizomes).
  • Seed is the main means of spread. Seed is spread in water and soil, and as a contaminant of agricultural produce.
  • Spread within patches occurs from rhizome growth and stems which develop roots near the base. Cultivation, earthworks and roadside machinery can spread fragments of rhizomes to clean areas where the fragments produce new plants.

Avoid the introduction of square-stemmed St John's wort

  • Preventing the introduction of square-stemmed St John's wort to clean areas is the best means of control.
  • Avoid spreading seed or fragments of rhizome in mud when using machinery and vehicles used in infested areas.
  • 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 square-stemmed 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 square-stemmed 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.

Cultivation

  • Square-stemmed 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.

Chemical control

Herbicides for Square-Stemmed St John's Wort Control

Herbicides for Square-Stemmed St John's Wort Control


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To the extent permitted by law, the Tasmanian Department of Primary Industries, Parks, Water and Environment (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using information or material (in part or in whole) contained on this website.

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