The Grains Research and Development Corporation (GRDC), led by Australia’s national science agency CSIRO, has enabled evidence-based increases to zinc phosphide (ZnP) mouse baits to aid grain growers battling above-average mouse numbers in eastern Australia via a recent research investment.
ZnP-coated wheat bait is the only registered in-crop rodenticide for the management of mice damage in broad-scale agriculture in Australia. The new Australian Pesticides and Veterinary Authority (APVMA) emergency use permit increases the concentration of zinc phosphide active per wheat grain from 25mg/kg to 50mg/kg, while still applied on-farm at 1kg/ha. This inevitably increases the likelihood of a mouse consuming a lethal dose in a single feed.
The GRDC/CSIRO research is the first laboratory-based wild house mouse bait efficacy study conducted in Australia since the chemical was first registered for use 20 years ago. Industry body Grain Producers Australia (GPA) applied for the APVMA emergency use permit based on the research outcomes.
CSIRO researcher Steve Henry, who led the study, said the lab results indicated the new bait was lethal in all mice while the previous bait used was only lethal in 50 per cent of mice.
“Our lab research has shown that mice rapidly develop aversion to the bait, meaning that if they do not consume a lethal dose from one grain of bait, they will not consume any more toxic grain,” Henry said.
GRDC Pests Manager Leigh Nelson said the increase in bait mixing concentration was expected to be well received by the industry, particularly given the current high volume of mice in eastern Australia ahead of winter crop planting.
“Current farming practices that conserve water and are environmentally sustainable, such as minimum or zero tillage, result in a significant increase in both available shelter and alternative food sources for mice,” he said.
“Mouse management requires an integrated approach and a key part of this is the reduction of alternative food sources, such as grain being left in the paddock post-harvest.
“This residual grain greatly reduces the probability of a mouse encountering and consuming a treated grain. So even with the increased bait mixing concentration, growers will still need to ensure they implement best practice tactics on farm for effective mouse control.”
The success of the permit application follows two emergency permit approvals from the APVMA in recent weeks approving additional uses of ZnP for mouse control. One will allow growers to apply 25g ZnP per kg of grain bait products at 1kg/ha to bare ground prior to planting – growers have previously required some ground cover to apply bait. The other will allow growers to protect crops sown into stubbles or thick ground cover by applying 25g ZnP per kg of grain bait products at rates of 3-5kg/ha.
The efficacy research followed the Organisation for Economic Co-operation and Development (OECD) guidelines and was approved by a CSIRO Animal Ethics Committee.
“GRDC and CSIRO will continue to undertake research to inform and improve grain growers’ management decisions and options for mouse control,” Nelson said.