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Prickly acacia (Vachellia nilotica)

A thorny tree that has invaded millions of hectares of Mitchell grass downs in western Queensland, turning open grassland into thorny woodland.

Key facts

Type: Weed, tree.

Native to: Africa and the Indian subcontinent.

Established in: QLD, NT, WA.

Other names: Acacia nilotica.

Identification

  • Shrub or tree to 10 m, with paired white thorns up to 5 cm long.
  • Fern-like leaves with many small leaflets.
  • Golden yellow ball flowers and grey, velvety pods constricted between seeds like a string of beads.
  • Look-alike: Mesquite has finger-like flower spikes; native acacias lack paired thorns.

Where it grows

Mitchell grass downs, bore drains, watercourses and floodplains.

Why it matters

  • Reduces grass production.
  • Restricts mustering and access to water.
  • Changes open grassland ecosystems.

How it spreads

  • Cattle and other animals eat the pods and pass seed in dung.
  • Floodwater.

Control options

  • Basal bark, foliar or soil-applied registered herbicides.
  • Mechanical clearing and fire, followed by follow-up control.
  • Hold stock that have eaten pods before moving them.

Hygiene and washdown

  • Hold livestock from infested paddocks for several days before moving to clean country.
  • 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): Weed of National Significance. One of 32 nationally agreed priority weeds, managed through national strategies with all states and territories.
  • Queensland: Restricted matter, category 3. Do not give it away, sell or release it into the environment. 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: Restricted weed. 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: Declared pest (C2), prohibited. C2 Eradication: present in limited areas and targeted for eradication. 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, 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)
  • 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