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Cactus control in the SA Arid Lands

Cactus control in the SA Arid Lands

There are 14 Opuntioid cacti species that can be found in the SA Arid Lands region. Each of them are Weeds of National Significance (WoNS) and are also declared weeds in South Australia. Under the Landscape SA Act 2019, landholders are obliged to control Opuntioid cacti species. It is an offence to possess, buy or sell these plants or to transport them on road without a permit.

There are no native cacti species in Australia.

Why control cactus?

Cactus can spread by seed or vegetatively, meaning detached cladodes can establish roots and grow. They outcompete native vegetation and left untreated, cactus infestations can spread until they smother natural species. The sharp spines can pose a threat to animals (both native and stock) and birds and seriously injure people. Cactus can also get caught in wool, devaluing it and posing a risk to shearers.

Forms of control

There is no single 'silver bullet' to cactus control. In the SA Arid Lands region there are three main forms of control - biocontrol, chemical and mechanical. Integrating a variety of methods offers the best chance of achieving effective control.

Two biocontrols – cochineal and cactoblastis – are most effective in dense infestations. They may take a few years to reduce or eliminate cacti populations but despite this, they can save significant time and resources. Herbicide control of outliers around dense infestations assist in preventing further spread of cacti. Physical removal and appropriate disposal of small isolated plants also helps to prevent cacti infestations spreading.

Cochineal

Cochineal (Dactylopius spp.) is a small insect, less than 1mm in size that feeds on cactus sap. The insect has a 55-day breeding cycle and can produce up to 2000 offspring in each, during warm conditions. Cochineal create a white fluffy substance on the outside of cladodes and produce a red dye when squashed.

Cochineal is spread through a cactus population or to new populations by the wind. Spreading infected cladodes manually can also greatly increase the rate of spread.

Cochineal is active during warmer weather and drier months, typically October to April in the SA Arid Lands region.

There are different species and lineages of cochineal that are suited to different cacti species. It is important to ensure the right cochineal species is used for Opuntioid cacti infestations. Prickly pear, Devil’s rope and Hudson’s pear all have individual cochineal species, however Riverina pear, Wheel cactus and Engelmann’s prickly pear all share the same cochineal species.

Your Community Landscape Officer can help identify Opuntioid cacti species on your property.

Cactoblastis Moth

Cactoblastis caterpillars (Cactoblastis cactorium) feed inside cladodes and are more effective in cooler and humid summer seasons. Cactoblastis is spread by moths flying to new populations and laying eggs and the process can be supported by physically moving eggs or caterpillars. Evidence of cactoblastis include piles of amber castings from caterpillars and dead cladodes looking shredded.

Other methods

Herbicides play an important part in Opuntioid cactus control. In an integrated management plan, where biocontrol is used on dense cacti infestations, herbicide is useful in treating outlier and isolated plants. In species that don’t have a known biocontrol, herbicide is the main method of control.

The two main methods of herbicide control used on Opuntioid cacti are stem /pad injection or herbicide spraying.

Stem/pad injection is useful on accessible open flat pad cacti (e.g. Opuntia robusta). Glyphosate is injected into every 2-4 pads on the plant using a drill or drenching needle. However, if the plant is too large or is difficult to access, this method becomes difficult and less effective.

Herbicide spraying with a number of different recommended chemicals (herbicides) can be effective. However, it is important to cover all pad/cladode surfaces on the plant to gain effective control. On large, multi-branched, wide plants this can be very difficult. Be prepared to carry out follow up control (probably three or four times) if you use this method. The PIRSA website is the best source of information about chemical control for specific opuntia species.

Chemical and mechanical control is the best option for small and isolated populations. Herbicide can either be applied with foliar spray or stem injected. It is important that total coverage is achieved when spraying and follow-up control is always necessary. Red marker dye can be useful to ensure no segments or plants are missed.

Herbicide is most effective when plants are actively growing in warm weather and not under stress from heat, drought or cold conditions.

Manual control

This method of control involves digging up the plants and burying. Care must be taken, as detached segments can easily regrow. Material can be disposed of by burial at least one metre deep or dried on a surface that is not soil, and burnt.

This method is more practical for small plants and scattered infestations. Mechanical removal is also an option for large, impenetrable stands or for organic properties, where chemical use is not an option, although biocontrol is an option in this instance. The main problem with this method is that if you don’t bury all pieces of the plants and/or pieces drop off when you try to move them to the burial site, new cacti will grow from the dropped pieces.


Opuntia species

Prickly pear (Opuntia stricta) grows to 2m tall and forms thickets. Its pads are grey-green and measure 10-25cm long. Spines are usually absent. Its yellow flowers measure 6cm in diameter and bears fleshy fruit that is purplish-red, globular to pear shaped and measuring up to 6cm long. Its seeds are fertile.

Biocontrol: Cochineal - species: Dactylopius opuntiae (USA lineage); Cactoblastis.

Riverina pear (Opuntia elata) has erect branches to 2m tall, sometimes with a purple tinge. Spines may be absent or 1-3 short spines can be present at some areoles. It features orange flowers and purplish-red club-shaped fruit to 6cm long.

Biocontrol: Cochineal - species: Dactylopius opuntiae(Mexican lineage)

Wheel cactus (Opuntia robusta) grows to 4m tall, but is usually found at 1-2m. It features flattened, circular blue green pads that grow up to 40cm wide. Between 2 and 12 spines are present per areole, each measuring up to 5cm. It has yellow flowers, 5-8cm in diameter and deep red fruits that are fleshy and globular shaped to 8cm long. Its seeds are fertile.

Biocontrol: Cochineal - species: Dactylopius opuntiae(Mexican lineage); Cactoblastis

Engelmann’s prickly pear (Opuntia engelmannii)is a low shrub to 1.5m tall featuring dense patches. Its pads are green, flattened and round to egg shaped measuring 15-20cm. There are 1-6 spines per areole, up to 1.4cm long. It has yellow flowers and purple egg-shaped fleshy fruit to 7cm long.

Biocontrol: Cochineal - species: Dactylopius opuntiae(Mexican lineage)

Devil’s rope (Cylindropuntia imbricata) is a deciduous, branched shrub 1-3m tall. Its pads are a dull grey-green 15-40cm long and 3.5-5cm thick. Each areole has between 2 and 12 spines, measuring 0.8-3cm long. It produces dark pink flowers and greenish-yellow egg-shaped fleshy fruit to 4cm long when ripe, and can form chains.

Biocontrol: Cochineal - species: Dactylopius tomentosus (Imbricata biotype)

Hudson’s pear (Cylindopuntia pallida) is a low spreading and deciduous shrub that grows to 0.5-2m. It has grey pale green pads, 4.5-26cm long and 1.3-3.5cm thick. Each areole has between 7 and 14 spines, each 1-4cm long. It produces pink to purple flowers and green to yellow-green fruit to 3cm long. Its seeds are sterile.

Biocontrol: Cochineal - species: Dactylopius tomentosus (Californica biotype)

Jumping cholla (Cylindropuntia prolifera) is a low shrub that grows to 0.4-1m Its spines are light to dark brown, 7–11 per areole measuring 1–2cm long and interlacing, with a white to light-tan sheath firmly attached. Its stem segments are dull-green to greenish-grey in colour and cylindrical, measuring 4-15cm long and 4-5cm wide. It has prominent segments that easily detach. It produces rose-magenta flowers 2.5-3cm wide and green fruit 2-5cm long.

Biocontrol: Cochineal - species: Dactylopius tomentosus (Californica biotype)

Coral cactus (Cylindropuntia fulgida var. mamillata) is a tree that grows to 3m tall. It has joints 6-23cm that are 2-3.5cm wide. It has up to 18 yellow or pale pink spines that age grown and features white or yellow sheaths. Six to 12 spines grow from each areole, which form a dense layer that obscures the stems. It has white and pink flowers, streaked with lavender and its green, fleshy, pear-shaped fruits grow to 4cm long, which produce flowers that become fruit in following years. It produces vegetatively.

Biocontrol: Cochineal - species: Dactylopius tomentosus (Cholla biotype)

Cylindropuntia spinosioris an erect shrub that grows to 1m tall. It often grows in patches several metres wide. It looks similar to Jumping cholla but it has a different spine and fruit colour. It has deciduous leaves. Mid grey-green cylindrical cladodes, 10-24cm long, 1.5-3cm diameter, firmly attached with prominent tubercles. Flowers are rose-purple in colour. Fruits are fleshy, cylindrical, to 4cm long, normally yellow but sometimes green. Each cladode has 6-24 spines, 0.8-1.5cm long, interlacing. The spines are white to grey with a white sheath firmly attached.

Biocontrol: Cochineal - species: Dactylopius tomentosus (bigelovii biotype)

Opuntia elatioris an erect, heavily-branched shrub that grows to 5m tall. It often grows in clumps. Pads are olive green, oblong shaped and 10-40cm long. Flowers are yellow-orange with red stripes. Fruit are egg-shaped and reddish when ripe. Each pad has 2-8 dark brown spines, 2-4cm long and needle like.

Biocontrol: Cochineal - species: Dactylopius opuntiae (Mexican lineage)

Drooping tree pear (Opuntia monocantha) is an erect shrub to 2m tall, sometimes with a short trunk. The plant has an obvious drooping appearance. Pads are glossy green, oblong to egg shaped, have a thin profile and are 10-30cm long. Flowers are yellow or orange-yellow. Fruit are pear shaped to 7cm long, red and spineless. Each pad has 1-2 brown to off-white spines, 2-4cm long.

Biocontrol: Cochineal - species: Dactylopius ceylonicus

Velvet pear (Opuntia tomentosa) is a shrubby to treelike plant up to 5m tall, often with a trunk. Segments and fruits are covered in fine hairs, giving a velvety appearance. Pads are oblong to egg shapes and 15-30cm long. Flowers are orange. Fruit is globular to egg shaped, red and up to 5cm long. Often this species is spineless but can have 0-4 whitish-yellow spines per pad, 0.5-1.5cm long.

Biocontrol: Cochineal - species: Dactylopius opuntiae (Lineage to be confirmed)

Bunny ears (Opuntia microdasys) is a branched shrub, forming thickets to 1m tall. Pads are green to pale green and velvety, round to oblong shaped and 6-15cm long. Pads are covered in distinctive clusters of yellow glochids. Flowers are yellow. Fruit are fleshy, globular shaped to 3cm long. They are red-purple and sterile. Spines are usually absent but 1 may be present.

Biocontrol: None known.

Opuntia sulphureais a multi-branched, low growing shrub that grows to 40cm high and 1.5-3m across in a clumping, circular formation. Pads are green to yellow-green, obovate, elliptical or sub-circular, 14-22cm long. The pads have elevated areoles that create a bumpy effect. Flowers are rich-yellow or sulphur-yellow. Fruit are red. Spines are often dirty white, 2-5cm long and numerous across the pad.

Biocontrol: None known..

How we’re supporting landholders

While cochineal was first released in the Flinders Ranges in about 2009 to tackle wheel cactus, the SA Arid Lands Landscape Board conducted its first cochineal trials on Coral cactus at Lake Everard in November 2017. The result of this trial was overwhelming, with almost all plants in the sizeable infestation dead.

Since then the board has extended its work with cochineal, recording similar results on infestations throughout the region, with 40 properties currently engaged across five different districts.

Breeding cochineal

A partnership between SA Arid Lands Landscape Board and Port Augusta City Council has allowed the tiny insect to be bred in a specially-designed nursery in the Australian Arid Lands Botanic Garden.

The nursery’s location allows easy access by the SA Arid Lands community and council staff. Prior to its development, the cochineal could only be harvested from cacti infestations in the region, which are often hundreds of kilometres away.

In the breeding nursery, infected opuntia pads are added to crates of fresh pads, allowing the cochineal to spread to clean material that can later be released on opuntia infestations in the field.

Four strains are bred at the facility that are specific to five cacti species found in the SA Arid Lands region: Wheel cactus (Opuntia robusta), Engelmann’s cactus (Opuntia engelmannii), Devil’s rope cactus (Cylindropuntia imbricata), Coral cactus (Cylindropuntia fulgida var. mamillata) and Jumping cholla (Cylindropuntia prolifera).