Pressure is growing on the APVMA from the grains sector to approve the use of 50 gram zinc phosphide baits, with an industry mouse expert saying the stronger baits are far and away the best option to tackle some already big mouse numbers across the country.
The APVMA received an application from Grain Producers Australia for a new minor use permit in November last year, which would allow growers to use 50 g/kg zinc phosphide for the control of mice.
The baits - double the strength of customary 25g/kg baits which are now considered largely ineffective - were previously given an emergency use permit by the APVMA but that expired as of January 1 this year.
A spokesperson from the APVMA said the application required "due assessment against the legislated criteria based on currently available information".
"The APVMA is prioritising this application and working with the applicant to make the decision as soon as possible," the spokesperson said.
While 25g/kg baits are still available, CSIRO mouse expert Steve Henry said they are now considered less than ideal to control mice particularly as cropping systems change.
He said one application of the 50g bait was "much more effective" for mice control than multiple applications of the 25g bait.
"In the past, when we were cultivating to control weeds and prepare a seed bed, there wasn't much other food that was left behind in the system for mice," he said.
"When the 25g/kg bait was spread, mice could easily find two, three, four grains of toxin making a lethal dose.
"With conservation tillage systems and more background food, it's really important that the first grain a mouse encounters is a lethal dose.
"From work in the laboratory and in the field, we know that if a mouse gets a sub-lethal dose it will stop taking the bait."
Grain Producers SA chief executive officer Brad Perry said the grower body had received contact from farmers concerned about not being able to access or use the 50g baits.
"There's no doubt an immediate decision needs to be made either way to provide some clarity for grain producers as we head into seeding," he said.
"My understanding is the double strength baits are in stock but the emergency permit by the APVMA expired late last year and therefore retailers are unable to sell them to grain producers until approval is reached - if it is."
Mr Perry said it was important grain growers had all the tools at their disposal to tackle mice.
"Mouse numbers are moderate in grain production areas of South Australia at the moment but if we continue to get rainfall, then it doesn't take much for mice numbers to grow rapidly, particularly with plenty of stubble around," he said.
"As is often said, prevention is better than the cure."
Dr Henry said while mice populations were patchy, some recent trapping on the Adelaide Plains had discovered up to 800 mice a hectare in certain paddocks.
He said there were also some high numbers on the Darling Downs in southern QLD.
While it is customary to bait around or after seeding, Dr Henry advised baiting whenever mice were present, making the 50g bait approval more pressing.
Grain Producers Australia, who applied for the minor use permit on behalf of the nation's grains sector, issued a statement about the situation late last week.
The advocacy group said it was working through "the correct processes with the APVMA and mouse bait manufacturers listed on the permit".
"The aim is to have this permit extended again to meet current demand," the statement said.
"Growers have indicated to GPA they're continuing to experience mouse activity on-farm and support the continued use of ZP50 through this permit to provide another, more effective option to help protect their crops from mouse damage."
