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Koster's curse (Clidemia hirta)

In Australia, Koster's Curse is known to have naturalised only near Julatten in north Queensland, where eradication steps were taken. It is highly invasive overseas and could threaten pastures, plantations, native vegetation and sensitive habitats if it establishes more widely.

Key facts

Type: Weed, shrub.

Native to: Tropical America, from southern Mexico to northern Argentina and the Caribbean islands.

Established in: QLD.

Other names: Soap Bush, Soapbush, Hairy Clidemia.

Best time to act: Treat before fruit set; flowering and fruiting may occur throughout the year in tropical climates elsewhere, but this timing has not been recorded for Australia.

Identification

  • This densely branching, long-lived shrub is usually 0.5–3 m tall and can reach 5 m in shaded areas.
  • Branches and leaves are covered with large, stiff brown or reddish hairs.
  • Opposite, oval leaves are 5–18 cm long and 3–8 cm wide, with finely toothed edges, a wrinkled appearance and five prominent, almost parallel veins.
  • Small white or occasionally pinkish flowers grow in clusters in the leaf forks or at branch tips; ripe berries are dark blue, purplish or blackish, hairy and 4–9 mm across.
  • Look-alike: No native or other naturalised species in Australia are reported as similar to Koster's Curse.

Where it grows

In Australia it is known to have naturalised near Julatten in northern Queensland, and humid coastal sites in the Northern Territory and much of north-east Queensland are within its potential distribution.

Why it matters

  • It can form dense thickets that smother plantations, pastures and native vegetation.
  • It has the potential to damage primary production, sensitive habitats and native plant communities, especially in the wet tropics.
  • In Hawaii it infests more than 40,000 hectares and threatens native species and ecosystems.
  • It is highly invasive in montane and cloud forests in several Pacific islands and is among the most problematic invasive species in parts of the Indian Ocean.

How it spreads

  • Berries can be dispersed by water, but birds are the most common dispersal method; a mature shrub can produce thousands of berries.
  • In Hawaii, berries have also been reported to spread by vehicles, people and pigs.
  • Bird and flood-borne seed dispersal was evident at the Julatten infestation.

Control options

  • Koster's Curse is targeted for national eradication in Australia, with programmes that map and monitor its distribution and coordinate or undertake eradication activities.
  • Manual weeding may work for small populations, but remove plants before fruit set.
  • Where a seed bank is established, follow-up work may be needed for up to ten years.
  • It is susceptible to a number of herbicides but can regenerate unless further applications are made; difficult access may prevent manual or spray control.

Hygiene and washdown

  • Berries have been reported to spread by vehicles and people in Hawaii, so avoid moving fruiting plant material between sites.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Restricted matter, categories 2, 3, 4, 5. Report it to Biosecurity Queensland within 24 hours; do not give it away, sell or release it into the environment; do not move it; do not keep it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)

Sources