Weed Alert: Prickly acacia
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- Declared in NSW under the Noxious Weeds Act 1993 (Current Status)
- Weed of National Significance (definition)
Contacts and Further InformationIf you find this weed please help to prevent its further spread by contacting your local Council Weeds Officer or the nearest NSW Department of Primary Industries office immediately for positive identification and further assistance.
Alternatively call the NSW Weeds Hotline on
1800 680 244 or send an email to firstname.lastname@example.org
Prickly acacia (Acacia nilotica)
Prickly acacia is an invasive thorny tree typically growing 4–5 m high. This weedy species can halve grassland productivity, interfere with stock mustering and restrict animal access to shade and water. Prickly acacia also impacts on the biodiversity of native grasslands, tourism and land use by indigenous people. This plant is one of the worst weeds in Australia due to its invasiveness, potential for spread, and economic and environmental impacts.
In the early 1900s, prickly acacia was planted as a shade and ornamental tree in the Bowen and Rockhampton districts of Queensland. In 1926, it was recommended to provide shade and fodder for sheep in western Queensland. The introduction of cattle into western Queensland and good wet seasons during the 1950s and 1970s saw this thorny tree invade vast areas of the Mitchell Grass Downs of central and western Queensland. Scattered infestations have been found along the Queensland coast, in the Northern Territory, north-eastern South Australia and the south-eastern Kimberley Ranges in Western Australia.
Prickly acacia is not currently known to be present in New South Wales (NSW), but has the potential to invade subtropical and grassland regions, including the North Western Plains.
Prickly acacia is a native tree of the tropics and subtropics. It is found in Ethiopia, Somalia, Pakistan, India and Burma and grows best in areas that have cracking clay soil with high water holding capacity. However, it can also grow on sandy soils when water is abundant and is commonly found on waterways and seasonal floodplains (350–1500 mm per annum).
Prickly acacia reproduces by seed (175 000 seeds per medium-sized tree each year). Pods and seeds can be moved in fast flowing water. Cattle can transport seeds long distances. They eat the ripe pods and excrete the seeds up to six days after consumption (at least 40% of seeds remain viable). The manure provides extra moisture and nutrients for seed germination and seedling growth. Goats and sheep chew the seeds and are less likely to spread them. If stock, particularly cattle, from affected areas of Queensland are brought into NSW they should be held in a quarantine area before and after transportation (for at least 7 days) to ensure excretion of viable seeds. The quarantine areas need to be checked for prickly acacia seedlings for seven years.
Prickly acacia is a spreading tree (4–5 m tall but sometimes reaching heights of 10 m), usually with a single-stemmed trunk that has several branches near the soil surface and a deep tap root. Young trees have bark tinged with orange and/or green. Mature trees have dark, rough bark and less thorny stems. Young stems have paired spines (1–5 cm long) at the base of each group of leaves.
Key identification features
- Leaves (30–40 cm long) are green and fern-like. Each leaf is made up of 10–25 pairs of very small (3–6 mm) leaflets.
- Flowers are bright yellow and wattle-like. Spherical flower heads (1–1.2 cm diameter) occur on 2 cm long stems. Groups of 2–6 flower heads are found at the base of each leaf joint.
- Seed pods (10–20 cm long) are flat, grey-green and covered in fine hairs. Mature pods darken to green or brown and have deep, irregular constrictions between each seed (8–10 seeds per pod). Seeds have a very hard brown seed coat.
Your local council weeds officer will assist with identification and information on control, removal and eradication of this weed. Infestations can be spread by inappropriate control activities. Individual plants can be manually removed but prickly acacia is capable of regenerating from cut stumps so all stumps and root material should be removed.
Prickly acacia is a Class 1 State Prohibited Weed across NSW under the Noxious Weeds Act 1993. It must be eradicated and land must be kept free of the plant. As a notifiable weed, all outbreaks must be reported to the local council within 24 hours, and the plant is prohibited from sale in NSW.
Adapted by AnDi Communications from the CRC for Australian Weed Management Weed Management Guide: Prickly acacia.
Reviewed by Peter Gray. Edited by Elissa van Oousterhout, Birgitte Verbeek.
- Spies P & March N (2004) Prickly Acacia National Case Studies Manual, Department of Natural Resources, Mines and Energy
- Declared Plant Policy (Government of South Australia), Prickly acacia (Acacia nilotica subsp. indica).