Prickly acacia

Prickly acacia is a declared Class A and Class C weed and a Weed of National Significance.

Go to the Weeds of National Significance website for more information.

Prickly acacia also has a statutory weed management plan (1.3 mb) which outlines the legal requirements for control.

Other names for this plant are Acacia nilotica or Vachellia nilotica.

Prickly acacia - infestation

Identification

You should use this as a guide. There may be other plants or weeds that look similar. 

If you are unsure, contact the Weed Management Branch.

Habit

These features describe the habit of this plant: 

  • fast growing
  • thorny
  • umbrella-shaped
  • grows up to 10m tall
  • can form dense thickets.

Prickly acacia - habit

Stems and branches

These features can identify the stems and branches:

  • 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.

Prickly acacia - stems and branches

Leaves

These features can identify the leaves:

  • four to 10 branches with 10 to 20 pairs of leaflets on each
  • leaflets about 6mm long by 1.5mm wide.

Prickly acacia - leaves

Flowers

These features can identify the flowers:

  • golden yellow
  • spherical heads
  • 1.2cm wide
  • borne on multiple stalks 2 to 4cm long
  • growing out of leaf joints.

Prickly acacia - flowers

Fruit and seeds

These features can identify fruit and seed:

  • very distinctive
  • 10 to 20cm long
  • soft and hairy
  • constricted between seeds
  • grey and green when ripe
  • break apart at the constricted points and separate into single seeded segments.

Prickly acacia - fruit and seeds

Similar looking plants

The following plant species look similar to prickly acacia:

Mimosa Bush

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

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

It is not a declared weed in the Northern Territory (NT).

This table (85.5 kb) can help you to identify a prickle bush that might be prickly acacia.

Impact 

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.

Habitat and distribution

Prickly acacia is native to the tropics and subtropics of Africa, Pakistan, India and Myanmar.

It was first imported into Australia as a shade and fodder tree.

It now prospers along water courses and out-competes native plants.

It is distributed from the New South Wales border, through Queensland, and across the NT to Western Australia’s Kimberley region.

It is found in scattered, isolated populations across the NT including the Barkly Tablelands and Katherine region, with a substantial infestation in the southern Victoria River district.

Spread prevention

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 doing all of the following:

  • map infestations to help develop a management plan
  • control minor infestations, isolated outbreaks or seedlings first
  • prioritise control along bore drains, creeks and dams to reduce spread
  • designate wash down areas and actively work to prevent contamination of clean areas
  • fence off stock from mature pods to contain infestations
  • quarantine stock when moving them from an infested area as seeds can take six days to pass through an animal
  • do not overgraze as healthy pasture will reduce the growth of seedlings
  • make sure imported stock are quarantined upon arrival to the NT or your property
  • monitor areas that you have treated and watch for re-infestations.

Prickly acacia - spread

Control

Chemical control

The best time to treat prickly acacia is from March to May. Below is a list of treatment methods that can be used.

Chemical and concentration Rate Situation, method and notes
Fluroxypyr 200g/L
Various trade names
750ml / 100 L Seedling (individuals or infestation) + adult (infestation):
Foliar spray - Uptake® Spraying Oil required
Fluroxypyr 333g/L
Starane™ Advanced
450 ml / 100 L Seedling (individuals or infestation) + adult (infestation):
Foliar spray - Uptake® Spraying Oil required
Metsulfuron-methyl 600g/kg
Various trade names
10g / 100 L Seedling (individuals or infestation) + adult (infestation):
Foliar spray - apply when actively growing, need wetting agent
Hexazinone 250g/L
Various trade names
4ml / spot
one spot for each
metre in height
Seedling (individuals or infestation) + adult (infestation):
Spot application - apply at the base of plant
Tebuthiuron 200g/kg
Various trade names
1.5g / m2 Seedling (individuals or infestation) + adult (infestation):
Granulated herbicide: ground applied – do not use within 30 m
of desirable trees or apply to single continuous area > 0.5 ha
Use higher rate on dense growth or heavy clay soils
Triclopyr 240 g/L +
Picloram 120 g/L
Access™
1 L / 60 L (diesel)
 
1 L / 60 L (diesel)
Adult (individuals or infestation):
Basal bark < 5cm stem diameter
Cut stump > 5cm stem diameter
Fluroxypyr 333g/L
Starane™ Advanced
900ml / 100 L
(diesel)
 
900ml / 100 L
(diesel)
Adult (individuals or infestation):
Basal bark < 10cm stem diameter, treat up to 45 cm from ground
Cut stump > 10cm stem diameter
Triclopyr 600g/L
Various trade names
1 L / 120 L (diesel)
1 L / 120 L (diesel)
Adult (individuals or infestation)
Basal bark < 5cm stem diameter
Cut stump > 5cm stem diameter

Non-chemical control

Hand pulling and grubbing

Weeds, including their roots, are physically 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, but it requires a lot of labour.

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 cannot 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, but 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 is used together with other methods. It is 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.

Last updated: 27 June 2017