Prickly acacia

• This thorny shrub or small tree usually grows to 5–10m tall.
• Thorns are paired, stout and generally 1–5cm long.
• Flowers are golden-yellow and ball-shaped. They grow on stems from leaf joints with 2–6 flowers per group.
• Leaves are fern-like, with 4–10 pairs of leaf branches and 10–20 pairs of narrow green leaflets on each branch.
• Pods are flat and 10–15cm long with narrow constrictions between seeds. They are greyish when ripe.
• Bark on saplings has a tinge of orange and/or green. Older trees have dark, rough bark.

3D model

• View the 3D model to help you identify this plant. You can magnify the image and manipulate the view to inspect the plant from every angle.

• There is potential for prickly acacia to grow in most areas of Queensland. About one-third of the state is well-adapted for prickly acacia growth.

• Visit Weeds Australia and click on the distribution tab to view the distribution map.

• Flowers year-round, mostly March to July.

Environmental

• Degrades soil by facilitating erosion.
• Threatens biodiversity through transformation of natural grasslands into thorny scrub and woodland.

Economic

• Decreases pastures and out-competes them for water.
• Forms dense thorny thickets that interfere with mustering, stock movement and access to water.
• Damages tyres (via thorns).

• Seeds spread primarily by livestock through ingesting mature pods. Long-distance movement is possible by livestock transport.
• Minor seed spread is by mud on vehicles and water movement.

• Find out how farmers can prevent weed spread.
• Find out how gardeners and outdoor enthusiasts can prevent weed spread.

Mechanical control

Grubbing

• This is ideal for large areas of scattered to medium-density infestations and is best done from May to September or before pod drop.
• Use a wheeled tractor of around 80hp with a scoop or grubbing attachment.
• It can be difficult to grub out trees greater than 15cm in diameter.

Blade ploughing

• Using a front-mounted blade plough (such as an Ellrott blade plough) is effective and efficient for medium-density infestations.
• Use this method from May to September only (to reduce establishment of seedling regrowth) or during drought conditions.

Pushing

• Pushing with dozers or loaders is useful for large areas of medium-density infestation.
• Use this method during drought conditions or from May to September only, to reduce establishment of seedling regrowth.
• Sometimes after pushing there is massive seedling emergence in areas around permanent waters and drainage lines.

Stickraking

• Use a stickrake with cutter bars attached to the bottom of tines.
• Use this method from May to September or during drought conditions.

Double chain pulling

• This method can be used for high densities of prickly acacia.
• It is effective against established stands but not for plants that have a basal diameter of less than 40mm.

Herbicide control

Basal bark treatment

• For stems up to 10cm diameter, carefully spray around the base of the plant to about 30cm above ground level. Thoroughly spray into all crevices.
• For large trees, spray up to 100cm above ground level.
• The best time for treatment is autumn.

Cut stump treatment

• Cut the stems off horizontally as close to the ground as possible.
• Immediately swab or spray the cut surface and stem with herbicide mixture.

Soil-applied treatments

• Soil-applied herbicides are taken up by plant roots after rainfall. The major benefit of this method is speed and ease of application.
• Apply the herbicides as close as possible to the trunk, preferably when rainfall is likely to occur within a few months.
• The best application period is October to January.

Foliar spray

• You can use foliar spraying for seedlings and young plants up to 2m tall.
• Use a fluroxypyr-based herbicide (such as Starane Advanced®) mixed with water and a wetting agent.

Read the prickly acacia fact sheet for herbicide control and application rates.

Physical control

Fire

• Prickly acacia is very tolerant of fire once it gets past seedling stage.

Irrigation channels

• Seek technical advice regarding options for treating channels such as bore drains.

Biological control

• In Queensland, 6 insects have been introduced as biological control agents against prickly acacia, with 2 establishing and providing some benefit.
• The beetle Bruchidius sahlbergi established successfully and is now widespread. Seed predation is generally low but may reach up to 80% where mature pods are available.
• The leaf-feeding caterpillar Chiasmia assimilis is not abundant in western Queensland but is exerting pressure on prickly acacia in coastal locations.
• Researchers continue to look for new biological control agents overseas, with India the current focus.

Native insect attack and dieback

• Prickly acacia is attacked by native insects associated with Australian native acacias and other native plants. Native insects can weaken prickly acacia and can contribute to the death of plants when other stresses are involved.
• Generally, leaf-feeding, sap-sucking, root-feeding, pod-feeding and seed-feeding insects attack actively growing prickly acacia.
• Bark-feeding and wood-feeding insects (including borers and twig-girdlers) prefer stressed and dying plants.
• Dieback of areas of prickly acacia has occurred occasionally throughout western Queensland infestations. Causal factors remain unclear but may involve:
  • soil-based pathogens
  • water stress during dry seasons and drought
  • high salt concentrations in soils
  • root predation by cicada nymphs
  • attack by other insects and diseases on stressed plants.

• Prickly acacia is a category 3 restricted invasive plant under the Biosecurity Act 2014. You must not:
  • give it away
  • sell it
  • release it into the environment.

If you do any of these, penalties may apply.

• You must take all reasonable and practical measures under your control to minimise the biosecurity risks associated with dealing with prickly acacia. This is part of your general biosecurity obligation.
• Each local government agency must have a biosecurity plan that covers invasive plants in its area. This plan may include actions to be taken on prickly acacia. Some of these actions may be required under local laws. Contact your local government for more information.