FIERCE debate continues to swirl surrounding the most effective bait for use in bringing the mouse plague under control.
One of the nation's peak grain grower bodies, Grain Producers Australia, has thrown its weight in behind the use of double strength zinc phosphide bait, on the back of CSIRO research finding it is more effective and has less risk of sub-lethal doses than the previously registered zinc phosphide bait.
The NSW government continues to push ahead with its application for an emergency permit for the use of the primarily domestic rodenticide bromadiolone in broadacre situations, in spite of concerns about off-target toxicity, with the product's high mortality rate a key factor in their desire to see it registered.
Now, the leader of one of the major manufacturers of agricultural mouse bait in the country has stepped into the discussion, claiming that the previously registered formulation of zinc phosphide remains suitable, saying the research showing it was not as effective as it needed to be was flawed.
Animal Control Technologies Australia (ACTA) managing director Linton Staples said while his company would be making double strength Mouse Off, its zinc phosphide based bait, he wanted to reassure farmers that the conventional 25 grams a kilogram zinc phosphide products were effective in most circumstances.
"With these Mouse Off products, more than 90 per cent of mice are killed within one or two days of application in most rural situations," Dr Staples said
"While some farmers do require second or third applications, as provided on the APVMA approved label, the vast majority of users achieve excellent results after one application with no non-target impact."
Dr Staples cast doubt on the CSIRO research that the established products had kill rates as low as 50pc, saying the research was based solely on laboratory data and claiming there had been some extrapolation which he said led to a misleading outcome.
"If this were the case, there would have been many fewer grain harvests over the last 24 years," Dr Staples said.
However, growers have welcomed the move towards stronger formulations of zinc phosphide.
Birchip, Victoria, grain grower Leigh Weir said, contrary to Dr Staples' claims, that the formulation needs to be beefed up.
He said he had been noticing a declining efficacy in standard bait over a number of years.
"We've been using bait extensively over recent years and we've really noticed that, in paddock conditions, the bait just hasn't been working," Mr Weir said.
"The efficacy has not been there and that has been particularly noticeable in certain conditions, when you're baiting in moist paddocks then it is definitely not performing," he said.
"In 2017 I baited six times and barely managed to protect the crop, it is a big cost and it is a big commitment in terms of time when you have so many other things to do to keep the crop going."
But Dr Staples said a wholesale switch to double strength bait may create a national shortage of supply.
He said COVID-19 had caused supply chain issues, in particular in securing sea freight to bring out the active ingredient zinc phosphide, and that there was a shortage that could hamper bait manufacturing.
"There was a risk of less crop area being protected if only double-dosed product is used," Dr Staples said.
"Industry needs to act with caution to ensure producing a higher dose Zinc Phosphide bait does not interrupt the supply of the current proven technology or crops could be lost as a result," he said.
In terms of utilising bromadiolone, Dr Staples said he understood the push for more products to be registered given the severity of the issue in NSW but urged caution.
"There are reasons why the permit for Bromadiolone grain bait use was withdrawn almost 10 years ago," he said.
"Bromadiolone takes up to eight days to kill a mouse, not the 24 hours claimed in various sources.
"During that time, the mice will continue to damage crops, but will also eat more doses of bait, even though the initial dose of bait will kill them eventually."
He said there could also be environmental issues due to the slow acting nature of the active ingredient.
"This extended feeding on bait can lead to accumulation of Bromadiolone in the mice.
"This means that if they are eaten by a domestic animal or native predator such as an owl or eagle, those animals may also accumulate a toxic dose in time."
Mr Weir said he was happy to let the Australian Pesticides and Veterinary Medicines Authority, the regulator for farm chemicals, assess the merits of bromadiolone.
"We're really keen to see how the double strength product works, as for the push for bromadiolone and whether that has a fit, it has to get its registration before we think of that, but we don't want a product that causes harm to off-target species."
Dr Staples said while the concern regarding off-target deaths was legitimate, the cost of doing nothing also had to be considered.
"Mice themselves are an environmental disaster," he said.
"They not only destroy crops and ruin valuable fodder reserves and damage farm equipment, but also destroy seed banks for native plant species and compete with native wildlife species for food."
A decision regarding the NSW government's application for an emergency permit for bromadiolone has yet to be handed down.