Prickly acacia

Prickly acacia already infests more than 6.6 million hectares of Australia.

It threatens agriculture and environment across most of northern Australia, including important production areas of the NT such as the Barkly tablelands.

Prickly acacia can have all of the following impacts:

• dense infestations can reduce pasture production
• thickets restrict mustering and restrict stock access to water
• infestations exclude native plants and animals reducing biodiversity
• thorns can damage vehicle tyres and injure animals.

To identify prickly acacia, you should use this as a guide:

• thorny, umbrella-shaped tree grows up to 10m tall and can form dense thickets
• single stemmed with spreading branches
• paired spines up to 5cm long at base of leaf stems (older stems may not have spines)
• smooth bark with a green and orange tinge (rough brown and black bark on older trees)
• four to 10 branches with 10 to 20 pairs of leaflets on each – leaflets about 6mm long by 1.5mm wide
• golden yellow flowers with spherical heads 1.2cm wide
• borne on multiple stalks 2cm to 4cm long growing out of leaf joints
• 10cm to 20cm long, soft and hairy, grey and green when ripe.

To help you identify a prickle bush that might be prickly acacia, read the what prickle bush is that? guide PDF (85.5 KB).

View a 3D interactive model of this weed below.

© Regional NSW through NSW DPI Invasive Species Biosecurity
Model created by Rachel Klyve

There may also be other plants or weeds that look similar below.

To find out more, get the prickly acacia weed note on the DEPWS website.

If you are unsure, contact the Weed Management Branch.

Similar looking plants

The following plant species look similar to prickly acacia:

Mesquite

Mesquite (Prosopis spp.) is native to North and South America.

Severe mesquite infestations can reduce the production of native and introduced pasture species by up to 90%.

Find out more about mesquite.

Parkinsonia

Parkinsonia (Parkinsonia aculeata) is native to central and South America, Mexico and southern USA.

It infests nearly 1 million hectares and threatens the agriculture and environmental values over three-quarters of the Australian mainland.

Find out more about parkinsonia.

Mimosa bush

Mimosa bush (Acacia farnesiana) is native to Central and South America.

It's a rounded shrub or small tree that forms thorny thickets that hinder mustering and stock access to water.

It's not a declared weed in the NT.

Mimosa

Mimosa (Mimosa pigra) is native to tropical America from Mexico to northern Argentina.

It's estimated that up to 140,000 hectares of land in the NT, 10% of the Territory's wetlands, is already impacted by mimosa.

Find out more about mimosa.

Chemical control

The best time to treat prickly acacia is from March to May.

See list of treatment methods that can be used in the table below.

Non-chemical control

For a list of non-chemical treatment methods you can use, read below.

Hand pulling and grubbing

Weeds including their roots are pulled out of the ground by hand or using hand tools. This is an effective method of control for individual weeds and recent outbreaks that haven't released seeds yet.

Blade ploughing

A blade plough is used to push over some woody shrubs and sever their roots underground. This exposes the roots and then buries the plant deep enough that it can't regenerate.

Stick raking

A large blade with teeth attached to a bulldozer is used to clear large weed infestations. This leaves large areas of soil exposed so follow up control or revegetation should be considered.

Chaining

A large heavy chain is dragged across the ground by heavy machinery to push over and pull out large weeds. This method is useful for removing roots and providing access for burning.

It works best at the end of the wet season when the ground is soft and roots are easier to pull from the soil. This method has been successful in prickly acacia control where dense stands are dry or in drought.

Fire

Fire as a management technique is most effective when it's used together with other methods. It's useful for mass seedling control if there is a sufficient fuel load.

Biocontrol

Biological control options have been researched in Queensland including tip boring moths, seed feeding beetles, leaf feeding beetles, caterpillars and bark and wood-feeding insects.

Prickly acacia seeds are distributed on the hair and hooves of cattle and when they pass intact through a cow's digestive tract.

Seeds are also spread by flowing water.

You can prevent the spread of prickly acacia by:

• mapping infestations to help develop a management plan
• controlling minor infestations, isolating outbreaks or seedlings first
• prioritising control along bore drains, creeks and dams to reduce spread
• designating wash down areas and actively working to prevent contamination of clean areas
• fencing off stock from mature pods to contain infestations
• quarantining stock when moving them from an infested area as seeds can take six days to pass through an animal
• not overgrazing as healthy pasture will reduce the growth of seedlings
• making sure imported stock are quarantined upon arrival to the NT or your property
• monitoring areas that you have treated and watch for re-infestations.