'The first plants of prickly pear species were brought into Australia on the First Fleet (Tanner, 2006b). Common pest pear was first recorded as being cultivated for stock fodder in the Parramatta district of NSW in the early 1800's (Tanner, 2006b).After the introduction and widespread planting of Opuntia species in Australia throughout the 1800‟s, an exponential increase in abundance and distribution of O. stricta was observed. Four million hectares of Queensland was infested with prickly pear by 1900, and by 1926, 24 million hectares was infested (Parsons and Cuthbertson 2001). It was estimated that some 12 million hectares of previously productive land was completely removed from productivity for 10-15 years during this time. At the peak of the infestation, it is estimated that prickly pear was spreading at the rate of 100 hectares an hour (Parsons and Cuthbertson 2001). A highly successful biological control agent, Cactoblastis cactorum, a stem boring moth was introduced, which achieved a 90% mortality of prickly pear between 1925 and 1933 (Parsons and Cuthbertson 2001).Various species of a cochineal mealy bug, Dactylopius spp., have also been introduced and can be effective in controlling common pest pear (Opuntia stricta), drooping prickly pear (Opuntia monacantha), and devil‟s rope cactus (Cylindropuntia imbricata) but less effective in controlling (Opuntia robusta), wheel cactus.' (Taken from the Opuntioid Cacti Management Plan, SA Government, 2009).
In the mallee region, several Opuntia species have established. In 2009 the Opuntioid Cacti Management Plan was published to help control these plants across South Australia.
A copy of the plan can be found here