Karroo thorn (Vachellia karroo)

PROHIBITED MATTER: If you see this plant report it. Call the NSW DPI Biosecurity Helpline 1800 680 244
Also known as: Karoo acacia

Karroo thorn is an adaptable, vigorous shrub or tree that forms dense, thorny thickets and is well suited to Australia’s rangelands.

Profile

How does this weed affect you?

Karroo thorn is an adaptable, vigorous shrub or tree that forms dense, thorny thickets and is well suited to Australia’s rangelands. It is fast growing, fire resistant and protected from browsing animals by its thorns. Karroo thorn is usually an evergreen tree, except during droughts or in very dry or cold localities, and grows to a height of 12 m.

Karroo thorn is identified as a threat to biodiversity. Dense thickets reduce agricultural productivity as they suppress the growth of grasses, prevent stock movement (including access to water) and add to the costs of mustering.

Where is it found?

It is present in southern Angola, Zambia, Zimbabwee and Mozambique and has been introduced into Libya, Morocco, Myanmar, India, Iraq, Corsica, Portugal, Sicily, Argentina, Bolivia, Chile, Paraguay, Spain and Mauritius. It is considered weedy in South Africa. Plant densities up to 2000 trees per hectare have been recorded in Eastern Cape Province.

As the favourite food of the black rhinoceros, it has been planted in botanic gardens and zoos in south eastern Australia to depict the African landscape. It was first recorded in Australia in Perth during the 1960s, possibly having spread from a residential planting or the Botanic Gardens. It was first recorded in NSW in Dubbo at Taronga Western Plains Zoo, but has since been eradicated. Currently there are no known infestations in NSW or Queensland.

Distribution map

How does it spread?

The spread of karroo thorn seed occurs by wind, water and animal droppings. Intentional cultivation by humans has also occurred. Large trees can produce as many as 19 000 seeds per year. These seeds can remain viable in the soil for at least seven years. Seed germination is improved when the outer seed casing is disturbed through means such as fire, passing through the digestive tract of an animal, or gradual weathering over time.

What does it look like?

Karroo thorn has paired thorns (up to 10 cm long but can be 25 cm long) that protect the leaves from browsing animals. In some plants the bark is reddish-brown to dark brown or black and rough. Other plants may have bark that is pale greyish-white or greyish-brown and smooth.

Key identification features

  • Leaves (12 cm long; 5 cm wide) are light green and fern-like with small oblong leaflets in 8 to 20 pairs.
  • Flowers (1–1.5 cm diameter) are sweetly scented, fluffy, yellow and ball-shaped (similar to Australian wattle flowers). They grow in clusters of 4 to 6 balls.
  • Seed pods (16 cm long; 1 cm wide) are sickle-shaped, woody and slightly constricted between the seeds.
  • Seeds (3.5–9 mm long; 2–7 mm wide) are shiny brown and can remain attached to the pod by a thread-like membrane.

Habitat

Karroo thorn is the most widespread acacia in southern Africa, growing under many soil, climate and altitude conditions, only limited by intense cold or lack of moisture. Its preferred habitat and climate are similar climate to the native grasslands of central New South Wales (NSW) and southern Queensland, giving it the potential to become established over most of subtropical and southern Australia. It is also common in the coastal dune forests of Natal and watercourses of the Karroo region of central Cape Province, indicating further potential to threaten riparian areas in many parts of Australia.

Acknowledgements

Adapted by AnDi Communications from the CRC for Australian Weed Management Weed Management Guide: Karroo thorn. Reviewed by Rod Ensbey and Peter Gray.

References

CRC Weed Management Guide

Weed risk assessment – Karroo thorn, The State of Queensland, Department of Employment, Economic Development and Innovation, 2011

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Control

Your local council weeds officer will assist with identification, control information and removal of this weed. Infestations can be spread by inappropriate control activities. Early detection and eradication will prevent the spread of this weed.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


PERMIT 9907 Expires 31/03/2020
Fluroxypyr 200 g/L (Starane™)
Rate: 35mL per L diesel/kerosene
Comments: Basal bark
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2020
Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 21 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2020
Glyphosate 360 g/L (Roundup®)
Rate: One part product to 1.5 parts water
Comments: Cut stump, drill, frill axe or injection
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2020
Glyphosate 360 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 1:1.5 glyphosate to water + 1 g metsulfuron to 1 L water
Comments: Stem injection
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area Duty
All of NSW General Biosecurity Duty
All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW Prohibited Matter
A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2018