Preventing Spread of Wheel Cactus

Preventing further infestations of Wheel Cactus is vitally important to the control and eradication of this weed. Therefore, the most critical action is to prevent the production of more fruit and seeds, and preventing birds and animals from eating the fruit and dispersing the seeds elsewhere.

The most effective methods, therefore, are to:

  • kill all mature, fruiting plants first
  • kill juvenile plants before they mature to fruit bearing age
  • remove fruit and dispose by incineration or burial

There are several different methods and tools we use to destroy Wheel Cactus plants, depending on their size, maturity and density, including:

Chemicals (Herbicides)
Manual Removal
Biological Control

Chemical Control

Using Glyphosate

Please exercise caution

  • wear protective clothing, gloves, boots and glasses to protect against the cactus prickles and herbicide
  • seek advice on how to correctly inject the cactus pads to prevent inhalation, ingestion or absorption of the herbicide

Medium – Large Plants

  • Inject all outer and second wheels (lobes) with 4ml of Herbicide (Glyphosate 450g/L diluted 1:3 in water)

Details of the injecting equipment used by the Tarrangower Cactus Control Group can be seen here. It is purchased through rural supply outlets.

(Injecting kits can be borrowed from the Tarrangower Cactus Control Group)

Please Do Not inject only the inner lobes, because the outer lobes will drop off onto the ground and re-root and re-grow.

Injecting Techniques

The key to a successful kill of a plant is using the correct injecting technique. The injector is inserted into the lobe (wheel), pushed well into the lobe and then pulled halfway out to make a pocket for the liquid herbicide. The gun then delivers a 4ml dose of herbicide into the lobe. Creating this pocket is very important as without it the herbicide will squirt back out of the lobe, causing danger to the operator and wasting herbicide. Injecting more lobes increases the chance of a faster knockdown and successful kill.

Small plants can also be injected, leaning the plant against a shoe for support and then injecting 1-2ml of herbicide into the lobe.

These photos show how to correctly inject from the side of the lobe of a wheel cactus to make a pocket for the glyphosate.

Chemical Control

Using Daconate

The Invasive Cacti Network South Australian field trip in May 2013 (see Post) included a demonstration of a very successful control method used on infestations of Wheel cactus in South Australia. This method consists of stem injection with Daconate (MSMA) where a hole is drilled into each base stem with a handheld power drill. An injector is then used to inject 4-6ml neat Daconate per stem. We were shown a plant that had been injected 3 weeks earlier and there was complete knockdown. Apparently there is no regrowth. Juvenile plants have a scratch made in the plant surface with the injector and a drop of Daconate is put on the scratch. There is complete knockdown and no regrowth.

Tarrangower Cactus Control Group has begun to explore Daconate as a potential control method for those with appropriate permits.

Manual Removal

Wheel Cactus plants are very easy to remove manually because they are very shallow rooted.
Also, it is possible to leave parts of the roots behind because they do not grow from the root fragments. 

Very Small Plants (less than 50 mm)

  • squash them under foot totally (until unrecognisable)

Small – Medium Plants

  • dig them up and dispose of the entire plant by burning (on a very hot fire) or burying under half metre soil
  • or take to them to the Maldon Recycle Station (Tip) for disposal (free of charge)

The tool we currently use is a perfect design for digging up small to medium sized plants, and can be purchased for a reasonable price from a ‘very common hardware chain’ store. The tool has two parallel points which can be used to uproot the plant and also has a flat blade which can be used to squash or cut the lobes.

Digging Hoe used by Tarrangower Cactus Control Group

(Digging tools and buckets can be borrowed from the Tarrangower Cactus Control Group)

DO NOT

  • dig up a wheel cactus plant and leave it lying on the ground
  • break off part of a lobe and leave it lying on ground
  • pick a cactus fruit and leave it lying on the ground as the fruit is full of viable seed

Any small piece of the plant, a wheel/pad or a flower can take root and grow into a new plant.

Please exercise caution: wear protective clothing, gloves, boots and glasses to protect against the cactus prickles.

Disposal

Because the Wheel Cactus plant is so extremely robust and drought resistant, it must be disposed of appropriately to ensure is dies. This cactus plant cannot be dug up or broken off and left lying on the ground to dehydrate and die; instead they will re-root and continue to grow. The plant can re-root from any pore on any lobe (pad/wheel) and so must be removed from contact with the soil. Hanging plants in trees or lying on rocks does not guarantee death.

Wheel Cactus growing from a tree.

Wheel Cactus plants removed manually should ideally be totally destroyed by incineration, however, most plants contain too much water for this to be a successful method, unless they are small, very dehydrated or you can create an extremely hot fire.

Manually removed plants can be buried, but need to be completely covered with soil and buried under a minimum 1/2 metre of soil.

Mechanical removal of Wheel Cactus has not proven successful because the plants break off and it’s very difficult to not leave fragments of plant on the ground. Each piece of plant with a pore (where the spine/prickle is on the pad/wheel) will grow into a new plant.

Biological Control – using Cochineal

A promising biological control method for Wheel Cactus (Opuntia robusta) is Cochineal insects (Dactylopius species). These herbivores attach to the outside of the host cactus plant and feed by sucking moisture from it.

From 1927-39, survey teams in Texas, Argentina and Mexico identified 56 biotypes of cochineal insects but only 17 of these became established in Australia. All look very similar to the naked eye but they are highly host specific, meaning they differ in terms of what species of cactus they will feed on. Hence, biological control of Wheel Cactus requires pairing the right Cochineal biotype to the right cactus species for a successful effect.

However, even pairing up a specific Cochineal with a specific cactus does not necessarily guarantee a successful relationship. Matching an Opuntiae Cochineal insect with an Opuntia cactus, such as Wheel Cactus, can fail because biotypes can be so highly evolved that local Cochineal populations only feed on local variants of a single Opuntia species. Harvesting Cochineal insects from one area and shifting it to another area may not result in successful colonization.

Despite these difficulties, Tarrangower Cactus Control Group is exploring biological control of local Wheel Cactus with Cochineal insects. However it is vital that all mature, fruiting Wheel Cactus plants continue to be killed using the herbicide injection technique. The Cochineal biological control may take 5 or more years to become established enough to have any significant effect. Therefore infestations producing new seed need to be controlled using current techniques. Hopefully in the future the use of Cochineal biological control will be an additional tool that can be used in combination with our current methods.

Cochineal insect Release 2011

Ian Grenda released some Cochineal insects (biotype unknown) to an area of Wheel Cactus in November 2011. He brought some Wheel Cactus pads infected with Cochineal insects from South Australia in the hope that the population of Cochineal would flourish in the Maldon and Baringhup region. However, two years later, the population numbers had not reached the critical mass required to have any significant impact.

Cochineal insect release 2013

In May 2013, TCCG members attended the Australian Invasive Cacti Network Field Day in SA. They visited a number of sites showing different cactus control methods. Internationally recognized biological control expert, Helmuth Zimmerman, shared his 50 years of experience to demonstrate the most effective way to harvest Cochineal insects and then transfer them into new cactus plants.

‘Biosecurity SA’ arranged permits to harvest Wheel Cactus pads infected with Cochineal insects and transport these to Victoria. These have been released in 3 sites with dense Wheel Cactus infestations in the Maldon and Baringhup region. The infected pads were placed lower down on the sheltered side of large Wheel Cactus plants, to protect the cochineal insects from prevailing winds and rain. The side of the Cochineal infested pad with the heavier colonies was laid directly in contact with a healthy pad on the host Wheel Cactus plant. The Cochineal infested pads were distributed every 50 metres or so, one pad per host plant.

The 3 sites will be monitored regularly, however it may take up to 5 years or more for the Cochineal population to increase and spread to infect new Wheel Cactus plants. The SA experience demonstrates the importance of regularly moving infected pads to new Wheel Cactus host plants in the area to build up the critical mass needed for effective biological control.

Cochineal release sites (May 2013)

Brochures

How to Kill Wheel Cactus

 

Videos

Equipment

Please click here for information about permits: Australian Pesticides and Veterinary Medicines Authority