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Beyond the Bale : June 2019
46 ON FARM While biological control of rabbits is very effective at reducing rabbit numbers, biological control alone is not enough. It is important to apply and integrate a number of control methods. In most situations, no single method will provide adequate control of rabbits in the long term. POPULATION KNOCKDOWN The first step is to reduce the rabbit population from medium–high densities down to a manageable level. This is usually done by biological control (via natural outbreak or deliberate release) and/or chemical control (eg a poison baiting program) during the non-breeding season. If RHD or myxomatosis are already present, then poison baiting should be delayed to allow the disease to reduce rabbit numbers. If rabbit density is low then extensive control can be started straight away. EXTENSIVE CONTROL The next part of the control program should destroy all source areas (where rabbits are living) and reduce rabbits to very low numbers. Control activities include warren ripping and destruction/ removal of harbours which provide rabbits with shelter, such as fallen logs, building debris or dense vegetation. Where the use of heavy machinery is not an option for warren ripping, alternative techniques such as explosives and fumigation may be used. Extensive control ensures that the rabbit population cannot recover quickly but it must be done thoroughly to ensure success. If any warrens or harbour are not destroyed, rabbit numbers will simply build up again. Sometimes rabbits can also dig back in and ‘re-open’ warrens if ripping is not done thoroughly (deep or wide enough) and the collapse of the warren structure is inadequate. MOP-UP ACTIVITIES There are usually small numbers of rabbits that survive extensive control, so advanced control is necessary for long-term management. This is where follow-up techniques such as fumigation, shooting and trapping are used in rabbit-active areas. INTEGRATED CONTROL METHODS The nationally coordinated release of the RHDV1 K5 rabbit biocontrol agent in 2017 – which saw an average 36% reduction in rabbit numbers at release sites – has been awarded one of the Australian Government’s top biosecurity awards. RABBIT BIOCONTROL IS A WINNER Rabbit eating carrots infected with RHDV1 K5. PHOTO: WA Government Rabbits are Australia’s most destructive agricultural pest animal and also threaten the survival of 321 native species. PHOTO: John Schilling A clip from the ‘Rabbit warren ripping and harbour destruction’ video available at www.wool.com/rabbits The strain of rabbit calicivirus (RHDV1 K5) was released during the first week of March 2017 at 323 locations across the country, as part of the RHD Boost project funded through the Invasive Animals CRC (now the Centre for Invasive Species Solutions (CISS)) with additional funding from AWI. It was the first nationally coordinated release of a new rabbit biocontrol agent in 20 years. After receiving pre- and post-release data from 230 participating release sites, the RHD Boost team has reported an average 36% decrease in wild rabbit numbers at the sites one month after the agent’s release (although not all sites experienced the same results). The CISS was awarded an Australian Biosecurity Award in March this year for its role in coordinating the release, monitoring and evaluation of RHDV1 K5. “The initiative was a massive combined effort with investment and support from the Australian Government, all state and territory governments, the CSIRO and the livestock industry through AWI and MLA,” CISS CEO Andreas Glanznig said. “The release was consistent with our Centre’s rabbit biocontrol pipeline strategy outlining the need for new and additional biocontrol tools every eight to ten years, to keep rabbit populations at bay.” AWI General Manager of Research Dr Jane Littlejohn reiterated the importance of industry support and investment to combat this introduced species. “Rabbits are agricultural and environmental vandals. They cost upwards of $250 million in lost agricultural production each year and threaten the survival of more native species than any other invasive species in Australia,” Jane said. “They actively compete with Australian livestock and native animals and – particularly during drought – can strip pastures bare. Just two rabbits per hectare are enough to stop plant regeneration,” Jane said. “The impact of rabbits would be much greater without myxomatosis and rabbit haemorrhagic disease being introduced into Australia. It has been estimated that biological control agents have resulted in RHDV1 K5 is available to purchase as a commercial product but is classified as a Schedule 4 restricted chemical product and can only be supplied to persons who are authorised to use the product under the laws of their state or territory. Check www.pestsmart.org.au/ purchasing-rhdv1-k5 for details.