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Physic nut (Jatropha curcas)

Physic nut has escaped cultivation in northern Australia and can form dense colonies that compete with native plants and pasture. Its seeds are highly poisonous to people, especially children, and are also toxic to livestock.

Key facts

Type: Weed, shrub.

Native to: Mexico, the Caribbean, Central America and South America.

Established in: QLD, NT.

Other names: Purging nut, Purging nut tree, Cuban physic nut, Barbados nut.

Best time to act: Look for germinating seedlings at the onset of the northern Australian wet season, usually October to December; flowering can occur year-round but is most abundant during the wet season.

Identification

  • An upright shrub or small tree, usually 2 to 4 m tall, with thick, softly woody stems.
  • Its shiny, dark green leaves are usually 10 to 15 cm long and 5 to 15 cm wide, with heart-shaped bases and three or five shallow, rounded lobes.
  • Small, pale yellow to greenish flowers grow in loose clusters in the forks of the upper leaves.
  • Its fleshy, oval or nearly round capsules are 3 to 4 cm long and change from green to yellow and then dark brown as they mature.
  • Capsules usually contain three hard, slightly kidney-shaped seeds, mostly brown or black with fine yellow stripes.
  • Look-alike: Bellyache bush (Jatropha gossypifolia) has reddish leaves covered in sticky hairs when young, and bright or dark red flower petals.
  • Look-alike: Castor oil plant (Ricinus communis) has leaves with seven to nine lobes and fruit capsules with numerous soft, blunt spines.

Where it grows

In Australia, it occurs mainly in disturbed sites, waste areas, abandoned gardens, pastures, open woodlands and roadsides in tropical and subtropical northern and north-eastern regions.

Why it matters

  • Fresh seeds are highly poisonous to humans, especially children, and can be mistaken for peanuts; they are also toxic to livestock.
  • It competes with native species and pasture plants and can form dense thickets or colonies.
  • If it establishes widespread populations, it may threaten biodiversity in some Australian rangeland communities.
  • It may act as an alternative host for insect pests of cotton crops.

How it spreads

  • It reproduces mainly by seed, though suckering can occur from tuberous roots and damaged crowns.
  • Ripe capsules split open and explosively release seeds, which can travel in water flows or in mud adhering to animals and vehicles.
  • Deliberate cultivation in home gardens has also aided its spread.

Control options

  • Dig out single plants and burn them, taking care to remove as much of the tuberous root system as possible.
  • For larger colonies, the cut-stump method is preferred: cut plants close to the soil surface and immediately swab the cut with registered herbicides.
  • Basal bark, soil injection and foliar application are also listed as effective herbicide application methods.
  • Check with the local council or state or territory government agency about control requirements.

Hygiene and washdown

  • Seeds can be moved in mud adhering to vehicles and animals, so avoid carrying mud from infested areas to clean 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: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • 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: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class A. Class A: to be eradicated. All declared weeds are also Class C, so they must not be brought into the NT.
  • 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)
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources