Wheel cactus (Opuntia robusta) has become a problem in the Upper Murray region, spreading slowly but surely across the hill tops around Greg Greg.
A native of Mexico, this invasive weed is thought to have entered the areas as a garden plant, and has been spread by birds and foxes who like its fruit.
New plants can also sprout from small pieces of cactus left on the ground.
Named for its wheel-shaped leaves, the wheel cactus is not controlled by the cactus moth (Cactoblastis cactorum), unlike the prickly pear cactus.
Wheel cactus is listed as a Weed of National Significance and has the potential to infest most of the arable land in southern Australia.
It is a very difficult plant to control, as the leaves are covered with a thick waxy coat and have very few openings (stomates) that allow herbicides in.
Landholders in the Upper Murray, in conjunction with Snowy Valleys Council and Murray Local Land Services, have trialled a direct-injection technique developed by the Tarrangower Weed Warriors in Victoria.
This approach has had some success, but unfortunately the very steep Upper Murray country is difficult to work on.
The lesson from this outbreak is to think carefully about what you introduce to your garden, particularly if you live in country areas, because it is so easy for introduced plants to escape.
Use of the cochineal insect (Dactylopius coccus) in the Flinders Ranges of South Australia has had some success controlling wheel cactus, and we are attempting to get it working for us at Greg Greg.
However these insects seem less adapted to the cold and rain than the cactus, which is still thriving.
The lesson from this outbreak is to think carefully about what you introduce to your garden, particularly if you live in country areas, because it is so easy for introduced plants to escape and cause serious headaches for land managers.
We will continue to work with landholders and local government to control this weed, and ask land managers to be vigilant in keeping an eye out for new infestations.
It is in the interests of all farmers that wheel cactus is managed effectively and prevented from spreading across the landscape.
For more information about wheel cactus, contact the Tumbarumba office of Murray Local Land Services on (02) 6948 9197.