CROPPERS in Australia's northern grain production zone are closely monitoring their first reasonable winter crop for three years following the big drought to ensure there is no mouse damage, with numbers building up to damaging levels.
Farmers in both Queensland and northern NSW farmers are being warned by pest management experts of a serious threat of mouse numbers building to economically damaging numbers this summer, both in terms of the winter crop nearly ready to harvest and newly planted summer crops.
The Grains Research and Development Corporation (GRDC), which is working on a mouse management program together with CSIRO, has issued advice suggesting that baiting will be required to stop the threat of crop loss.
CSIRO mouse researcher Steve Henry, whose work has support from the GRDC, is advising growers to closely monitor for mouse activity and bait to protect winter crops pre-harvest, as well as newly planted summer crops.
The rapid build-up of mouse numbers has caught some by surprise, coming immediately after a massive drought where numbers were very low, but Mr Henry said it was not an uncommon pattern.
He said protracted dry periods followed by significant rainfall - as has been experienced by many growers - was often the catalyst for a rapid increase in mouse populations in northern farming systems.
"In southern Queensland, we are receiving on-ground reports indicating mouse activity around Brookstead on the Darling Downs, as well as east of Dalby and in parts of the Goondiwindi, Moonie, Miles and Condamine regions, he said.
"Likewise in northern and central NSW, where we are getting reports of mouse numbers where there are quite reasonable winter crops.
"All it takes for seasons to favour mice is ample food and shelter, and given we have that this year I would anticipate that we will see numbers continue to increase."
In winter crops, Mr Henry's advice to growers is to be vigilant in assessing mouse numbers and bait where there is evidence of activity or signs of crop damage.
He said mice caused issues in mature crops by climbing stems and chewing nodes, resulting in dropped heads.
If farmers are to bait Mr Henry said they would need to act fast to avoid problems delivering the grain due to chemical residue requirements.
"If growers are baiting in winter crops, it is imperative they keep in mind there is a 14-day withholding period for baiting with zinc phosphide prior to harvest," Mr Henry said.
For those who are planning or have planted summer crops, he advises being on the lookout for activity in paddocks and baiting if mice are present.
"We know that mouse damage often happens in the first 24 to 48 hours of planting so it is best to bait mice at or as soon as possible after the crop is sown," Mr Henry said.
Grower should monitor mice after baiting to ensure that they have achieved a reduction in mouse activity. Ongoing monitoring of crops through spring and summer is important to ensure that mouse numbers don't get out of control.
Given mouse numbers are expected to continue to increase through spring, Mr Henry encourages growers to talk with their retailer about sourcing zinc phosphide early to ensure they have what they need for effective management.
For growers needing to bait, Mr Henry advised them to apply bait according to the product label. Zinc phosphide bait must be spread according to the label rate of one kilogram per hectare.
He said of circumstances allowed to try to wait six weeks before re-application of bait to minimise the chance of bait aversion.
"This means mice that have previously tried the bait are more likely to try it again, and it also targets new mice in the population that are susceptible to the bait," he said.
He also encouraged growers to bait over large areas and to encourage neighbours to bait at the same time if they also have a mouse problem.
Mr Henry also urged farmers to report mouse clusters to authorities.
"I also urge growers to report and map mouse activity - presence and absence - using MouseAlert so other growers can see what activity is being observed locally and via Twitter using @MouseAlert," Mr Henry said.