Mouse numbers on the rise

Agricultural researchers are warning grain growers across the region about a potential threat of rising mouse numbers during the approaching sowing season.

They raised the issue at the latest Grains Research Development Corporation National Mouse Group meeting, identifying Australia’s southern cropping region as vulnerable.

Reports are that a combination of grain on the ground following strong wind before harvest last year and summer rain could promote a rapid increase in mouse populations in coming weeks.

Recent monitoring and trapping efforts have detected high rates of pregnancy in females – adding to concerns about the risk of crop damage at sowing.

National Mouse Group, which co-ordinates action to counter mouse plagues, includes researchers, advisers, growers and other industry stakeholders.

Grdc-supported mouse researcher Steve Henry from CSIRO told the meeting the combination of grain remaining in paddocks and good rain was leading to ideal mouse-breeding.

He added growers in some areas were already reporting increased mouse activity.

“Parts of the Wimmera and Mallee and South Australia’s Lower Eyre and Yorke peninsulas incurred significant head loss in November 2019 when severe winds struck,” he said.

Mr Henry said large quantities of grain on the surface of paddocks could reduce the chance of mice finding toxic bait, while at the same time providing them with an ongoing food supply.

“If strong winds have resulted in two tonnes per hectare of grain on the ground in some areas, that equates to up around 4000 grains per square metre,” he said.

“The challenge for growers is to reduce the food load for mice in stubbles.

“Putting sheep on stubbles and strategic cultivation – burying grain – will assist with food reduction, and growers should spray out any summer germinations. Seeding with knife points assists in burying residual seed – enhancing bait uptake.”

Mr Henry emphasised the importance of timing bait applications.

“It is critical that growers bait six weeks out from seeding if mouse numbers are reasonably high, and then follow up with another bait application off the back of the seeder if numbers are still high at sowing,” he said. “A six-week break between applications avoids the risk of bait aversion.”

Zinc phosphide bait must be spread according to the label rate of one kilogram per hectare.

Report sightings

Mr Henry urged growers to get into their paddocks to get an accurate understanding of conditions in terms of the amount of grain on the ground and signs of mouse activity. High stubble loads hide signs of mouse activity.

He said as summer spraying intensified, reports of mouse presence were expected to increase.

“I also urge growers to report and map mouse activity – presence and absence – using Mousealert, online at www.mousealert.org.au so other growers can see what activity is being observed in their neighbourhood and via Twitter using @Mousealert.”

The GRDC’S mouse-related research, development and extension program is continuing to reveal new insights about mice in Australian broadacre cropping systems.

CSIRO researchers have been undertaking trials to determine if they can enhance the uptake of zinc phosphide bait by testing potential new bait substrates that might be more attractive to mice. Researchers are testing the willingness of mice to transition from one food to another and then determining whether mice will continue to eat that alternative food source once zinc phosphide bait has been applied.

GRDC research investments have shown that: mice prefer cereals over lentils; background food significantly affects consumption of bait; and strategic use of bait is more effective than frequent use of bait.

The next phase of the research will examine the role of available alternative food on commercial zinc phosphide bait effectiveness.

Research also includes a focus on mouse ecology. This work will involve a series of experiments aimed at understanding how mice function in zero and no-till cropping systems.

Mouse ecology research will address five key topics – farming practices, managing refuge habitat, understanding mouse movements, mouse burrows and bait delivery.

Data generated is providing evidence that under modern conservation farming systems, mice are remaining in paddocks year-round and establishing large burrow systems.

In previous conventional tillage cropping systems, mice would move to fence lines for habitat after harvest.