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Karoo acacia (Vachellia karroo)

Karoo acacia is a thorny tree that can form dense thickets, displace other plants and restrict movement. It is prohibited matter in NSW, where suspected plants must be reported immediately and must not be sold.

Key facts

Type: Weed, tree.

Native to: Southern Africa.

Established in: QLD, NSW, VIC, WA.

Other names: Karroo thorn.

Best time to act: Look for the conspicuous yellow flowers in summer, and report any suspected plant immediately whenever it is found.

Identification

  • It is an evergreen tree or shrub that can grow to 12 m tall, though it may lose its leaves in very dry or cold conditions.
  • Its fern-like leaves are up to 12 cm long, with several pairs of leaf segments and small, light-green leaflets.
  • Straight white spines grow in pairs at the leaf bases; they are usually about 10 cm long and can reach 25 cm.
  • Sweetly scented, fluffy yellow flower balls, 1–1.5 cm across, grow in clusters of four to six.
  • Its flattened, crescent-shaped pods are green and shiny when young, then turn brown and woody; they can grow to 16 cm long.
  • Look-alike: Mimosa bush (Vachellia farnesiana) has much shorter prickles and cigar-shaped pods, while prickly acacia (Vachellia nilotica) has shorter spines and greyish-green pods with obvious constrictions between the seeds.
  • Look-alike: Giraffe thorn (Vachellia erioloba) has shorter spines and half-moon-shaped pods; umbrella thorn (Vachellia tortilis) has a mix of white and curved brown spines and strongly coiled pods.

Where it grows

In Australia, it has been planted in botanical gardens and zoos, with those plants eradicated; central NSW grasslands and riparian areas are considered potential invasion habitats.

Why it matters

  • Dense, thorny thickets can injure people, livestock, pets and wildlife and restrict movement or make mustering difficult.
  • The thickets suppress grasses, reducing grazing productivity, and can block access to waterways.
  • They suppress native vegetation and reduce food and habitat for native wildlife.

How it spreads

  • Plants can produce fruit within two years, and large trees can produce up to 19,000 seeds a year; seeds can remain viable in soil for at least seven years.
  • Germination is improved by fire, weathering and passage through an animal's gut.
  • Seeds can travel in animal droppings, especially livestock droppings, and seeds or pods can also move through waterways or short distances by wind.

Control options

  • Do not attempt to treat or dispose of a suspected plant yourself; report it immediately to the relevant state biosecurity authority. In NSW, call the NSW Biosecurity Helpline on 1800 680 244.
  • In NSW, the Department of Primary Industries and Regional Development leads the initial response and treatment or disposal to prevent spread.
  • Agency-listed treatment options include basal-bark, cut-stump and stem-injection herbicide methods; these should be used only as part of an authorised response and in line with current labels and permits.
  • Arrange follow-up checks through the biosecurity response to look for regrowth and new seedlings.

Hygiene and washdown

  • Avoid moving pods, seeds or contaminated soil, and clean vehicles, machinery, boots and other gear before leaving a site where the plant is suspected.
  • Take care not to carry pods or seeds in livestock, fodder or equipment.
  • 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): National priority exotic pest. On the National Priority List of Exotic Environmental Pests, Weeds and Diseases, so any new detection should be reported straight away. National Environmental Alert List. One of 28 weeds named on the National Environmental Alert List as early-stage invaders with serious potential to harm the environment.
  • Queensland: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with 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: State prohibited weed. State prohibited weeds are the highest priority: the Victorian Government is responsible for eradicating them, so report any sighting to Agriculture Victoria.
  • 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: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • 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
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources