Smooth tree pear (Opuntia monacantha)

Also known as: prickly pear, drooping prickly pear, drooping tree pear, cactus, cacti

Smooth tree pear is an upright cactus with smooth, glossy oval-shaped stems. It forms dense infestations and has sharp spines that can injure people and animals.

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How does this weed affect you?

Smooth tree pear is an invasive spiny cactus. The spines can:

• injure people, livestock, working dogs and pets
• injure and sometimes kill native animals that gets trapped in the spines
• get stuck around the mouth of lambs or calves and stop them feeding
• devalue wool and hides
• prevent shearing.

Dense thickets of smooth tree pear restrict the movement of animals and people, so that:

• livestock cannot move to areas with better pasture
• mustering is difficult
• access to watering points is reduced
• recreation such as bushwalking or bird watching becomes difficult.

Smooth tree pear also:

• competes with native plants
• invades native pastures reducing productivity
• harbours pests including foxes, rabbits and fruit fly.

What does it look like?

Smooth tree pear is an upright cactus up to 6 m tall though usually only 2 – 3 m. The stems have an obvious drooping appearance. It sometimes has a short woody trunk with clusters of large spines up to 10 cm long. Smooth pear tree leaves are very small and drop off, so are rarely seen.

Pads (also called stems or cladodes) are:

• light green
• 10–45 cm long and 6–15 cm wide
• 4–6 mm thick
• glossy
• egg to oblong-shaped
• often elongated
• drooping, especially higher on the plant.

Cacti pads have bumps on the surface called areoles. Barbed bristles (glochids), spines, leaves, flowers, fruit, roots and new shoots all grow out of the areoles.

Areoles:

• are widely spaced
• usually have 1–2 spines in each but increasing to 4–5 in older parts of the plant
• have short, brownish woolly hairs and brown barbed bristles

 Spines are:

• 1–5 cm long
• off white, yellowish or red-brown.

Flowers are:

• yellow with outer petals often having red stripes
• up to 6 cm in diameter
• present from October onwards, but peak during summer.

Fruit are:

• green, ripening to red-purple
• 4–7 cm long
• pear-shaped
• pulpy with reddish flesh
• spineless but have barbed bristles
• mostly grow on the margins of the stems
• often joined, forming chains of fruit.

Seeds are:

• yellow or pale brown
• smooth and round
• 3–4 mm in diameter.

Roots are:

• fibrous
• shallow.

Varieties and forms

Smooth tree pear plants can vary naturally in colour, shape and size.  Some of these forms and varieties are intentionally selected and cultivated by collectors, growers and sellers.  

• Opuntia monacantha var variegata is a variety of smooth tree pear that is marbled with combinations of white, cream, yellow, light green and sometimes pink colours.
• Opuntia monacantha f. monstrosa is a form of smooth tree pear that has stretched, tortured and distorted looking pads.
• Opuntia monacantha f. monstrosa variegata “Joseph’s Coat” is a form of smooth tree pear that also has variations in colour.

The biosecurity duty applies to all variations and forms. They must not be imported into the state, sold, bartered, exchanged or offered for sale.

Similar looking plants

Smooth tree pear looks similar to the following weed speed species:

• Common pear (Opuntia stricta), which is shorter than smooth tree pear and has thicker, dull, pale green or grey-green stems.
• Indian fig (Opuntia ficus-indica), which is usually taller than smooth tree pear and has larger, usually spineless stems. It has larger flowers and the fruit have barbed bristles.
• Velvet tree pear (Opuntia tomentosa) which has fine, often velvety, hairs on the stems and fruit and orange-red flowers.

Where is it found?

Smooth tree pear grows from coastal NSW to the Western region.

It is native to South America.

What type of environment does it grow in?

Smooth tree pear mostly grows in subtropical, semi-arid and warmer temperate climates. It tolerates a wide variety of soil types though it is often found on sandy soils including coastal dunes. It grows in pastures, open woodlands, waterways, roadsides, railways and coastal areas.

Maps and records

• Recorded presence of Smooth tree pear during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  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

Birds and other animals eat the fruit and spread the seeds in their droppings.

By plant parts

Stems can break off the plant and be distributed by animals, vehicles or moving water. Immature fruit will also grow into new plants.

References

Harvey, K.J., McConnachie, A.J. Sullivan, P. Holtkamp, R. and Officer, D. (2021). Biological control of weeds: a practitioner's guide for south east Australia. New South Wales Department of Primary Industries, Orange.

Lim, T. K. (2012). Opuntia monacantha. In Edible Medicinal and Non-medicinal Plants (pp. 683-686). Springer, Dordrecht.

Parsons, W. T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. CSIRO publishing.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 5 May 2021 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Opuntia~monacantha

Sheehan, M. R., & Potter, S. (2017). Managing Opuntioid Cacti in Australia: Best Practice Control Manual for Austrocylindropuntia, Cylindropuntia and Opuntia Species. Department of Primary Industries and Regional Development.

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.

To manage smooth tree pear:

• control all plants in small or isolated infestations
• safely dispose of all plant parts
• distribute biological control agents.

Prevention

Do not grow smooth tree pear in gardens or pots. Do not take cuttings of unknown cactus plants to grow out or share with others.

Stop the spread of cactus into new areas by checking clothing, vehicles and equipment for plant parts before leaving an area that has any cactus weeds.

Physical removal

By hand

Dig up small or isolated plants using a mattock or other tools. Wear appropriate protective clothing and gloves to protect against injuries.

By machine

Dense infestations or large isolated plants can be removed with machinery where there is good access to the site, the site is not environmentally sensitive and plant parts can be safely disposed of.

Disposal

Dispose of smooth tree pear plants by burying at least 1 m deep or by burning in a hot fire. Contact your local council for information about other disposal options.

Biological control

The cochineal Dactylopius ceylonicus provides good control of smooth tree pear. It takes several years to kill plants. Control is slower in areas with high rainfall.

Felling plants over 2 m tall and stacking the cut segments after the cochineal has established will speed up control.

There are several species and linages of cochineal insects that look similar, but they each control different cacti. It is important to use the right species of cochineal for each species of cactus. Contact your local council weeds officer for information about using cochineal to control smooth tree cactus. The cactoblastis moth (Cactoblastis cactorum) and soft rot pathogens (e.g. Phyllosticta concava) attack smooth tree pear and limit growth but do not control it.

Chemical control

Spot spraying

Herbicides are especially useful for sparse, scattered infestations. Spray actively growing plants. Cover all parts of the plant with herbicide to the point of visible wetness. Check treated plants and control new growth.

Herbicide options

See Using herbicides for more information.

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Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 500 mL in 100 L of water
Comments: Spray actively growing plants. Thoroughly cover all of the plant with herbicide mix to the point of runoff. Regrowth may occur, so a follow-up application may be necessary. To improve uptake, add a paraffinic oil e.g. Uptake®, Titan Paraffin or Apparent Paraffinic spraying oil at the rate of 500 mL per 100 L of water.
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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Triclopyr 240 g/L + Picloram 120 g/L (Access™ )
Rate: 1 L per 60 L of diesel.
Comments: Apply as an overall spray, wetting all areas of the plant to ground level.
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: 500 mL in 100 L of water
Comments: Apply to actively growing plants. Spray actively growing plants. To improve uptake, add a paraffinic oil e.g. Uptake®, Titan Paraffin or Apparent Paraffinic spraying oil at the rate of 500 mL per 100 L of water.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Triclopyr 600 g/L (Garlon® 600)
Rate: 800 mL per 60 L of diesel
Comments: Apply as thorough foliage spray.
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 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.
Central Tablelands	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. 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.
Central West	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. 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.
Hunter	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. 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.
Murray	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. 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.
Western	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. 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 2023