Black locust (Robinia pseudoacacia)

Black locust is a hardy, spiny tree up to 25 m tall. It is poisonous to people and animals.

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How does this weed affect you?

Black locust:

• is poisonous to people and livestock
• forms dense thickets that outcompete native plants
• reduces food and habitat for native animals
• restricts access for people and animals
• releases chemicals from its leaves that may prevent other plants from growing.

Human poisoning

All parts of the plant are poisonous, especially the pods, seeds, bark and leaves. They contain proteins called robin and robitin. These are not life-threatening but can cause:

• dizziness, convulsions and drowsiness
• nausea, vomiting and diarrhea
• cold extremities
• pupil dilation.

 What to do if a person is poisoned:

• If the patient is unconscious, unresponsive or having difficulty breathing dial 000 or get to the emergency section of a hospital immediately.
• If the patient is conscious and responsive call the Poisons Information Centre on 13 11 26 or your doctor.

Livestock poisoning

Black locust is poisonous to livestock, including sheep, horses and cattle. Horses are affected the most. It can cause:

• breathing difficulties
• loss of appetite
• fatigue and paralysis
• cold extremities
• pupil dilation

Recovery takes several days. It can kill animals though this is not common.

What does it look like?

Black locust is a fast-growing deciduous tree. It produces suckers from the roots and can grow in dense, spiky walls. It usually grows to around 10-15 m tall but can get up to 25 m.

Leaves

The leaves are up to 15 cm long and made up of 11–21 leaflets. There is one leaflet at the end and the rest are in opposite pairs.

Leaflets are

• bright green turning yellow in autumn
• 2–5 cm long and 1.0–2.5 cm wide
• oval shaped often with a notch at the tip
• smooth on the edges
• sparsely hairy when young and smooth when older
• present in spring and early summer.

Spines are:

• in pairs
• 5–­­25 mm long
• at the base of some of the leaves.

Flowers are:

• white, occasionally pink or purple
• pea-like
• strong smelling
• in drooping clusters about 10–15 cm long.

Fruit are:

• smooth, shiny, leathery pods
• 3–8 cm long and 1.0–1.5 cm wide
• green when young brow when mature.

Seeds are:

• hard
• 3–5 mm long
• dark brown or black.

Stems:

• smooth barked when young then deeply furrowed when older
• thorny when small
• reddish-greenish brown.

Roots are:

• usually, shallow
• fibrous and sometimes spiny
• large, underground systems
• easily able to form new plants by suckering.

Similar looking plants

Black locust is similar to:

• Honey locust (Gleditsia triacanthos), which has smaller flowers, slightly toothed leaf edges, larger seed pods (15–40 cm long) and larger seeds (1 cm long).
• Tree of Heaven (Ailanthus altissima), which haslarger leaves (20–35 cm long), no spines and winged seed pods.

Where is it found?

In NSW, black locust grows in coastal regions of NSW from the North Coast to the South East. It has also been found in the Northern and Central Tablelands and Riverina regions.

Black locust is a native plant in the United States of America. There are records of trees in NSW dating back to the 1850s and it was probably introduced as an ornamental tree.

It is a weed in New Zealand, Canada, South America, Europe, Africa and Asia.

What type of environment does it grow in?

Black locust grows in temperate and sub-tropical areas. Trees grow best in full sun and well-drained soil. They do not grow well in shade or waterlogged soils.

Plants grow:

• along waterways
• in woodlands and forests
• urban bushland
• disturbed sites such as roadsides and gardens.

Maps and records

• Recorded presence of Black locust during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

Black locust has been planted in gardens and used as root stock in grafted trees e.g. golden robinia  Robinia pseudoacacia ‘Frisia’.

By seeds

Trees take 6 years to produce fruit. Seeds usually germinate in spring, though they may remain dormant for many years. Seedlings are fast growing but don’t grow well in shade or compete well with other plants.

By plant parts

Back locust produces suckers from, roots and stumps. Disturbance or damage to roots by mowers, whipper snippers, digging or fire can cause the plant to sucker vigorously. Roots left in the soil can regrow a long time after the main plant has been removed. Grafted varieties of trees that used black locust for root stock can also sucker and spread if the roots stock is disturbed by cutting.

References

Gibbons, W., Haynes, R. R., & Thomas, J. L. (1990). Poisonous plants and venomous animals of Alabama and adjoining states. University of Alabama Press.

Identic and Lucid (2016). Weeds of Australia: Robinia pseudoacacia L. Retrieved 13 November 2023 from: https://keyserver.lucidcentral.org/weeds/data/media/Html/robinia_pseudoacacia.htm

Martin, G. D. (2019). Addressing geographical bias: A review of Robinia pseudoacacia (black locust) in the Southern Hemisphere. South African Journal of Botany, 125, 481-492.

McKenzie, R. (2012). Australia's poisonous plants, fungi and cyanobacteria: a guide to species of medical and veterinary importance. CSIRO.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 13 November 2023 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Robinia~pseudoacacia

Richardson F.J.,Richardson R.G. and Shepherd R.C.H (2006).Weeds of the south-east an identification guide for Australia. R.G. and F.J. Richardson, Melbourne.

More information

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Control

Controlling black locust can be difficult because of its strong root system. Plants often re-sprout or sucker. Combining several control options is usually the most effective way to kill black locust.

Check treated sites for a few years to make sure plants are dead. They may need to be re-treated more than once.

Prevention

Don’t plant black locust or other Robinia varieties.

Avoid moving soil, vehicles and machinery contaminated with black locust roots or seeds.

Minimise disturbance in areas near black locust infestations because they establish quickly in these situations.

Grow plants for shade and competition to reduce the chance of black locust spreading into new areas.

Early detection

Learn to identify black locust and remove plants early to reduce the chance of spread. Small, individual plants are easier to dig up.

Slashing and mowing

Root suckers can be slashed or brush cut, but this will only suppress growth, not kill the plant. Cutting suckers down over many years may eventually exhaust the root system. These activities might also encourage seeds to grow.

Physical removal

Seedlings can be hand pulled or dug out but it can be hard to tell a seedling from a sucker. Suckers:

• have sharp spines
• cannot be easily pulled up or dug out
• regrow very easily.

Wear gloves to protect yourself from sharp spines. Large trees and thickets can be cut down with a chainsaw or pushed over with a bulldozer. Roots and stumps can be removed with tractors and other large machinery. Treat cut stumps with herbicides to prevent them from sprouting.

Disposal

Contact your local council for information about how to dispose of black locust material.

Chemical control

If treating regrowth wait till the plants have regrown at least 1 m.

Basal bark

Treat actively growing dry trunks or stems.

Spray or paint the herbicide mixture around the base of each stem from ground level to a height of at least 30 cm (50 cm for best results) from the ground. Wet the bark to the point of runoff. Old rough bark will require more herbicide mixture than smooth or young thin bark.

Cut stump

Cut the stem low to the ground, less than 15 cm if possible. Apply the herbicide mixture to the cut stump and the sides of the stump within 15 seconds.

Stem injection

Drill downward holes into the trunk all the way around the tree. Alternatively, make cuts with a saw or axe all the way around the trunk. Fill each hole or cut with herbicide within 15 seconds.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 200 g/L (Various products)
Rate: 35 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock feed for 7 days after application. See label for further information.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 21 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: One part product to 1.5 parts water
Comments: Cut stump, drill, frill axe or injection
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
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: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
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 pest 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.
Hunter An exclusion zone is established for all land in the region, except the core infestation which includes all urban centres of the Hunter region.	Regional Recommended Measure* (for Regional Priority - Containment) Entire Hunter Local Land Services region: Land managers should mitigate the risk of the plant being introduced to their land. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Core infestation: Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
North Coast Exclusion (eradication) zone: Coffs Harbour City LGA, Lord Howe Island,` Bellingen Shire LGA, Kempsey Shire LGA, Nambucca Valley LGA. Core infestation (containment) zone: Ballina Shire LGA, Byron Shire LGA, Clarence Valley LGA, Kyogle Shire LGA, Lismore City LGA, Port Macquarie-Hastings LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2024