How To Manage It?
Best practice management
When controlling Opuntia Prickly Pear species, an integrated weed management approach is usually desirable especially for larger infestations.
Chemical control: While several herbicides are recommended for managing Prickly Pears, chemical control is not always effective, as many species occur on rocky slopes, and infested areas must be checked and resprayed over several years if necessary (Parsons & Cuthbertson 2001). Methods used are:
- Foliar spray covering all pads
- Stem injection (includes drill and fill method on every 2-3 pads)
- Basal bark and cut stump (not normally used or considered best practice).
However, plants are extremely hardy and follow up and monitoring may be required for 1-2 years to ensure plant do not re-sprout. Registered herbicides, techniques and on-label instruction should always be followed in your state or territory. A variety of herbicides (chemicals) are know to be effective. Please see Sheehan & Potter (2017) for an overview. Also see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au. Permits from state or territory Environment Protection Authorities may be required if herbicides are to be sprayed on riverbanks.
Non-chemical control: Physical control: Physical control either by manual (hand) or mechanical (machine) removal can be feasible and cost-effective for all species of Opuntia (Prickly Pears).
Manual (hand) removal appears to be one of the most effective control methods for for scattered and small infestations (Sheehan & Potter 2017). However, the spines make manual removal of these species difficult (Parsons & Cuthbertson 2001). Using tools and avoiding spines and glochids is a top health and safety concern when working with Prickly Pears. Personal Protective Equipment (PPE) must (should) be worn, and tools used that eliminate or significantly reducing handling of plants with spines and glochids used.
Mechanical (machine removal) is useful for large dense impenetrable stands (Sheehan & Potter 2017). This method is useful for removing bio-mass and increases accessibility for other follow-up control methods. Machine removal with front end loaders causes high levels of disturbance and will require planning and long term follow-up using an integrated weed management techniques for cacti and other weeds that could colonise the area. Normally mechanical control should be carried out when conditions are dry to avoid damaging soil reducing soil disturbance, reducing likely spread of plants. However caution should be employed as some species have glochids that are airborne and are more likely to dislodges and injure workers with PPE like masks or respirators worn with eye protection
Disposal: Care must also be taken to remove and properly dispose of plants parts. Pads, flowers, fruits and even small sections of stems if left on the soil surface can produce roots and grow into a new plant. If one larges plant is uprooted, broken up, and left on the soil surface, each pad will take root and form a new plant. Where one plant was present there would now be many plants. The root system must also be dug out to prevent regrowth (Parsons & Cuthbertson 2001). Plant can be buried at a depth of 1 metre on or off site. Burning plants (all vegetative, flowering and fruiting parts) with other dry materials for plants thahave dried out over summer can also be used to kill plants. However, you should consult you local fire service for advice and permissions.
Fire: The effect of fire on Prickly Pears are not well understood. For some species it has been shown that fire is not effective in killing all plants and they can recover with great vigour. In addition, fire and strong winds are thought to spread the stem segments of some species aiding spread (Sheehan & Potter 2017).
Biological control: Biological control using Cactoblastis moths or Cochineal insects can be effective on dense populations, and outlying plants can be infected by transferring infected pads to them (Parsons & Cuthbertson 2001). However, there are a number of species of Cochineal insects that are host specific, and may destroy one species of Opuntia but not others (R. Chinnock, pers. comm.). The effect of these agents appears to be limited in colder climates (Muyt 2001). Correct identification of Opuntia species is required so the host specific biological control can be used. Further information can be found in Sheehan & Potter (2017).
Does it have a biological control agent?
YES. Twenty species of biocontrol agents have been released against prickly pears. Ongoing work to identify which cochineal agents can be utilised against previously untested Opuntia species and how biocontrol can be optimised through integrated weed management practices (Harvey, et al 2023).
When does it grow? (lifecycle/growth calendar)
All Prickly Pears reproduce from broken-off stem segments which develop roots from lower areoles (spots on the stem segments) that are in contact with the soil surface. Detached plant parts from some species have been known to last up to 3 years indoors.
Most Prickly Pears that occur in Australia can also reproduce by seed. Seeds germinate any time of year and plants generally flower at three years old. All Prickly Pears are long lived (Parsons & Cuthbertson 2001).