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Caltrop (Tribulus terrestris)

Caltrop is a widespread weed in mainland Australia that competes with other plants in crops, pastures, orchards and disturbed areas. Its hard, spiny fruits can injure people and animals, damage bicycle tyres and contaminate produce, wool and crops.

Key facts

Type: Weed, herb.

Native to: Generally accepted as native to southern Europe and northern Africa, though its native range is uncertain..

Established in: QLD, NSW, ACT, VIC, SA, WA, NT.

Other names: Goat’s Head, Puncture Vine, Bindii, Doublegee.

Best time to act: Look for seedlings after rain in late spring and summer, and treat them early when herbicides are most effective.

Identification

  • It is a low, mat-forming annual herb with branched stems up to 1 m long, usually prostrate in Australia.
  • Its pinnate leaves are usually opposite and have a silvery, hairy appearance.
  • Bright yellow flowers, 5–15 mm across, grow singly from leaf axils and open in the morning.
  • The nearly spherical, woody burrs are 6–10 mm long and break into five nutlets with sharp, rigid spines.
  • Look-alike: Tribulus cistoides is a more robust, coastal northern Australian species with larger flowers, whose petals are more than 15 mm long, and fruits that are more or less hairless.
  • Look-alike: Tribulus eichlerianus is generally distinguished by its distinctively shaped, densely hairy fruits.

Where it grows

In Australia, caltrop is widespread across mainland states and territories, growing in crops, orchards, vineyards, overgrazed pastures, roadsides, stockyards and other open, disturbed places, especially where soils are dry and sandy.

Why it matters

  • Its mat-like growth can cover a large area, out-compete other plants and may inhibit the growth of nearby plants.
  • The spiny fruits can injure people and the feet of horses, sheep, cattle and dogs, and can pierce thin shoe soles and bicycle tyres.
  • Caltrop foliage is toxic to livestock, especially sheep, and grazing has been associated with nitrate poisoning, photosensitisation and sheep staggers.
  • Fruits can contaminate crops and dried fruit or become embedded in sheep’s wool, lowering its value.

How it spreads

  • Caltrop spreads by seed in its spiny nutlets, which can attach to animals, vehicle tyres, footwear and clothing.
  • Nutlets can also become embedded in wool, and roadworks, contaminated produce and machinery can help spread them.

Control options

  • Aim to reduce seed production and dispersal, and remove individual plants as they emerge.
  • Hand-pull small seedlings; bag fruits removed from larger plants and dispose of them in a bin, or dry and burn them if local rules permit.
  • Use registered herbicides at the seedling stage; fruits present on treated plants may still contain viable seed.
  • Collect mature fruits mechanically where appropriate, and maintain or re-establish dense ground cover to compete with seedlings.

Hygiene and washdown

  • Remove nutlets from footwear, tyres and clothing after leaving an infested area.
  • Check hay, produce, stock, soil and machinery brought onto a property for nutlets.
  • 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: Regionally prohibited / regionally controlled / restricted weed (varies by region). Where it is regionally prohibited, landowners must take all reasonable steps to eradicate it on their land. Where it is regionally controlled, landowners must take all reasonable steps to prevent its growth and spread on their land. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • 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: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • 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)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources