Mesquite (Prosopis species)

Also known as: algaroba, honey mesquite, velvet mesquite

Mesquites are spiny trees or shrubs with fern like leaves and yellow flowers. They form thorny thickets that can restrict movement of people and animals.

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How does this weed affect you?

Mesquite trees:

• outcompete native plants
• reduce habitat for native animals
• outcompete pasture species, reducing productivity
• form impenetrable, thorny thickets that restrict movement of people and animals
• restrict access to water for livestock and native animals
• have long spines which can injure people and animals, and puncture tyres
• use large quantities of water and reduce runoff in arid areas.

What does it look like?

There are three species of Prosopis in NSW:

• Honey mesquite (P. glandulosa var. glandulosa)
• Velvet mesquite (P. velutina)
• Algaroba (P. pallida).

Another mesquite, (P. juliflora) is present in Australia but not NSW. There are also hybrids of mesquites, which can make identification difficult.

The following description covers the Prosopis genus.

Mesquites may be multi-stemmed shrubs 3–5 m tall or single-stemmed trees with a spreading canopy growing to 15 m tall. Single branches grow out past the main canopy giving the plant an untidy appearance. Plants can live for over 100 years.

Leaves are:

• fern-like
• made up of many small leaflets, which may be oval or long and narrow. Sizes vary between species with the leaflets on:
  • honey mesquite up to 4.5 cm long
  • velvet mesquite up to 12 mm long
  • algaroba up to 10 mm long
• usually, dark green but can be bluish green
• alternate along the stem.

Honey mesquite is deciduous in cold climates.

Flowers are:

• greenish yellow
• grouped together densely in cylindrical spikes up to 10 cm long
• present in spring and summer.

Seed pods are:

• green when young
• straw-coloured or purplish when mature
• up to 20 cm long
• smooth (hairy on velvet mesquite)
• straight or curved
• slightly constricted between each of the seeds.

The number of seeds varies between species:

• Honey mesquite produces 5–18 seeds per pod
• Velvet mesquite produces 10–17 seeds per pod
• Algaroba produces up to 30 seeds per pod. 

Spines:

• grow from where the leaf stalk joins the stem
• are in pairs and up to 4 cm long on velvet mesquite 
• are solitary and up to 6 cm long on honey mesquite 
• are in pairs (up to 1.5 cm long) or absent on algaroba.

Branches are:

• zigzagged and sometimes drooping
• smooth and dark red–green when young
• rough and grey when older.

Roots:

• are extensive
• include a deep taproot.

Similar looking plants

Mesquite looks like:

• Karoo acacia (Vachellia karroo), which has much larger spines (up to 25 cm long) and pompom like flowers.
• Mimosa bush (Vachellia farnesiana), which has cigar–shaped seed pods.
• Prickly acacia (Vachellia nilotica), which has pompom shaped flowers. This plant has not yet been found in NSW.
• Parkinsonia (Parkinsonia aculeata), which has flowers with five petals, short, curved spines (up to 1 cm long) and does not have fern–like leaves.

Where is it found?

Mesquite plants could invade all areas of western NSW. Currently the range of locations varies for each species:

• Velvet mesquite has been found growing in the Western, Central West, North West, Riverina and Murray regions. It is common throughout the Broken Hill and Milparinka areas.
• Honey mesquite grows in the Murray and Western regions.
• Algaroba has been found in the Western region near the Queensland border, north of Bourke.

Mesquites are native to USA, Mexico and northern parts of South America. They were introduced to Australia as fodder and shade trees in the late 1890’s.

What type of environment do they grow in?

Mesquites grow in tropical, subtropical and semi-arid climates. Plants can tolerate a wide range of harsh conditions including high temperatures, drought, highly saline and alkaline conditions. They can grow in a wide range of soils including poor soils such as iron stone and cracking clays where little native vegetation grows. 

Maps and records

• Recorded presence of Mesquite during property inspections (Map: Biosecurity Information System - Weeds, 2017-2026)
  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?

By seed

Mesquite plants usually start producing seeds when they are 2–5 years old. Trees can produce hundreds of thousands of seeds. Seeds may remain dormant in dry soil for over 10 years.

Seeds are spread by animals and flood waters. Cattle, horses, sheep, goats, donkeys, pigs, emus and kangaroos have all been observed eating the seeds. The viability of the seeds after they pass through an animal’s digestive tract, varies between species. Seeds are more likely to germinate if eaten by cattle rather than sheep. Fire and wet conditions can enhance germination.

References

Anderson, L. J., van Klinken, R. D., Parr, R. J., Climas, R., & Barton, D. (2006, September). Integrated management of hybrid mesquite: a collaborative fight against one of Australia’s worst woody weeds. In Fifth Australian Weeds Conference, Papers and Proceedings (pp. 24-28). Adelaide, Australia. Adelaide: Weed Management Society of South Australia Inc.

Parsons, W.T. and Cuthbertson, E.G. (2001). Noxious weeds of Australia, second edn, CSIRO Publishing, Collingwood, Melbourne.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 14 March 2024 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Prosopis

Queensland Department of Agriculture and Fisheries. (2020). Restricted plant fact sheet: Mesquite (Prosopis spp.) Retrieved 14 March 2024 from: https://www.daf.qld.gov.au/__data/assets/pdf_file/0004/73489/mesquite.pdf

Van Klinken, R.D. & Campbell (2009). Prosopis L. species In The Biology of Australian Weeds Vol 3. Ed F.D. Panetta. R.G. and F.J. Richardson. Melbourne.

More information

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Control

Successful weed control requires follow up after the initial efforts. This means looking for and killing regrowth or new seedlings. Using a combination of control methods is usually more successful.

Preventing spread

If possible, remove trees and shrubs when they are young before they have started producing seed pods. In summer, remove livestock from paddocks with mature seed pods. Hold stock from mesquite areas in a clean paddock for at least one week before moving them. Check the holding paddock for seedlings.

Check for new plants each year as seeds can stay dormant for over 10 years.

Physical removal

By machine

For all mechanical control methods, it is important to remove the bud zone of the root system, which is about 30 cm deep. If this is not removed, the plant can regrow

Mechanical methods include:

• Stick raking, which is most effective on medium to high density infestations of algaroba. A stick rake with cutter bars is attached onto a dozer.
• Dozer pushing has been successful for algaroba but is less effective on multi–stemmed species, which often break off at the ground and reshoot.
• Blade ploughs can be very effective on all mesquite species. The implement must be set at a depth of 30 cm.
• Grubbing implements sever the root base below the crown and/or physically remove plants from the soil.
• Chain pulling using dozers may kill up to 90% of trees in a mesquite infestation. It is not as effective for very dense infestations or for very young plants. It is also not recommended on velvet mesquite. Follow up with fire may be needed. After pulling, rest paddocks to allow grass to build up before burning. It is better if burning can be delayed until seedlings have germinated, as they will be killed by the fire.

Fire

Fire effectively kills algaroba mature trees and seedlings. Medium density infestations are the optimum for fire control. Fire may not kill all of an infestation because of uneven fuel loads. Follow up may be needed for new seedlings or surviving plants.

Biological control

Two biological control agents were released in NSW for mesquite control from 1998 to 2000:

• A leaf tying moth (Evippe sp.#1), which is rare in NSW but reduces flowering, seed set and general plant growth.
• A psyllid (Prosopidopsylla flava), which has established in northwest NSW.

These agents are not available for redistribution.

Chemical control

Foliar spray 

Spray seedlings to flowering plants but do not spray plants with pods. Spray leaves and stems to the point of runoff. A wetting agent will improve uptake of the herbicide.

Basal bark

Basal bark application is suitable for plants with stems less than 5 cm diameter at the base. Spray the bark all the way around the stem from ground level to 30 cm high, wetting thoroughly to the point of runoff.

Cut stump

This method is suitable for plants with stems up to and over 5 cm in diameter at the base. Cut stems off as close to the ground as possible and apply herbicide within 15 seconds.

Gel herbicide: Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm.

Stem injection

Make a series of cuts 15-20 mm deep around the trunk using an axe or saw. Space cuts evenly with no more than a 20-40 mm gap between them. Apply a 5 mm layer of gel over the lower surface of the cut.

Herbicide options

See Using herbicides for more information.

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Aminocyclopyrachlor 240 g/L (Method® 240 SL)
Rate: 0.5 mL undiluted per cut
Comments: Stem inject: make equally spaced downward cuts into the stem to make pockets large enough to hold the herbicide. Apply the herbicide dose to each cut.
Withholding period: Nil for domestic grazing. See label for livestock export conditions.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon® Extra)
Rate: 350 mL per 100 L of water For best results add a wetting agent: 100 mL/100 L of water
Comments: Controls seedlings, plants in full leaf and flowering before podding. Thoroughly wet all foliage, stems and soil around the base of the plants. Do not spray plants bearing pods. Wetting agent: BS1000 Biodegradable Surfactant or equivalent.
Withholding period: Where product is used to control woody weeds in pastures there is a restriction of 12 weeks for use of treated pastures for making hay and silage; using hay or other plant material for compost, mulch or mushroom substrate; or using animal waste from animals grazing on treated pastures for compost, mulching, or spreading on pasture/crops.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Picloram 44.7 g/L + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut stump for small plants: Apply a 3–5 mm layer of gel onto stems less than 2 cm diameter. Apply 5 mm layer on stems above 2 cm diameter. Stem inject trees: Make evenly spaced cuts 1.5-2 cm deep around the trunk. Apply a 5 mm layer of gel over the lower surface of the cut.t.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 240 g/L + Picloram 120 g/L (Access™ )
Rate: 1.0 L in 60 L of diesel (or biodiesel such as Biosafe).
Comments: Basal bark plants with stems less than 5 cm diameter at the base. Spray the bark around the stem from ground level to 30 cm high, wetting thoroughly to the point of runoff. Cut stump application for plants with stems up to and over 5 cm in diameter.
Withholding period: Nil
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 350 mL in 100 L of water. For best results add a wetter at 100 mL/100 L of water.
Comments: Controls seedlings, plants in full leaf and flowering before podding. Thoroughly wet all foliage, stems and soil around the base of the plants. Add a wetting agent to increase efficacy. Do not spray plants bearing pods.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the NSW 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.
All of NSW	Prohibition on certain dealings Must not be imported into the state, sold, bartered, exchanged or offered for sale. All species in the genus Prosopis have this requirement
Central West	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. 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. Notify local control authority if found.
North West	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. 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. Notify local control authority if found.
Riverina	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. 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. Notify local control authority if found. Your local biosecurity weeds officer can help to identify, advise on control, and how to remove this weed.
Western An exclusion zone is established for all lands in the Western Local Land Services region, except the core infestation area, which comprises all lands within the counties of Evelyn, Yantara, Mootwingee, Yancowinna, Menindee, Tandora, Livingstone and Windeyer.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers mitigate the risk of new weeds being introduced to their land. Within exclusion zone: 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. Notify local control authority if found. Within 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.
	*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 2025