Take home messages

• Mouse numbers are currently low across most regions of southern New South Wales, South Australia and northwest Victoria. At this stage, there is low potential for economic damage at sowing in 2019.
• Information about changes in mouse numbers in the lead up to the 2019 sowing can be accessed from the mouse monitoring updates.
• Growers should conduct their own monitoring to ensure they know what is happening in their paddocks in the lead up to sowing each autumn. This includes following the recommendations outlined in the GRDC GROWNOTES™, Tips and Tactics, Better Mouse Management page.
• Timely application of mouse bait at the prescribed rate is paramount for reducing the impact that mice have on crops at sowing. Strategic use of bait is more effective than frequent use of bait.
• GRDC has invested in a suite of new projects aimed at understanding the way mice use zero and no-till cropping systems and developing new strategies to monitor and control mice.

Background

There are three distinct but related GRDC investments that aim to better understand the way mice use zero and no-till cropping systems. The outcomes of these projects will lead to a reduced impact of mice in cropping systems through the development of more effective monitoring systems and better strategies to control mice using existing technology.

1. Surveillance and forecasts for mouse outbreaks in Australian cropping systems

This project commenced in October 2012 and the GRDC has invested in five years of additional monitoring. The aim of the project is to monitor mouse populations across all grain growing regions and use predictive models to forecast mouse outbreaks. A key element of the project is to communicate the results of the monitoring and predictions to growers and industry to enhance awareness of increases in mouse activity.A new component of this work is to develop and test the feasibility of a remote monitoring system for mice to detect changes in mouse activity throughout the year and at a spatial scale that is not possible using existing monitoring techniques.Preliminary exploratory work has started to test prototype monitoring systems. Once a suitable system has been identified, laboratory trials will be run using arenas to determine how efficiently mouse activity is detected. If the results in the laboratory are favourable, the monitor will be tested in enclosures with known numbers of wild mice and then in field-based scenarios. This work will begin in 2019 with field-based testing planned to commence in 2020.

2. Bait substrate trials

In recent years, growers have reported poor efficacy of zinc phosphide. It is not clear what is driving the reduced effectiveness of baits, but in some instances, growers are reporting the need for multiple applications of bait to achieve the desired level of control.Trials to determine what is driving the reduced efficacy of the bait and testing potential new bait substrates that might be more attractive to mice have commenced.

Experiment 1: Two choice grain preference

Experiment 1 is designed to test the willingness of house mice to switch food types when challenged with an alternative food type. This will determine if mice display a grain preference and identify leading bait substrate candidates. Mice were held on a background food type (barley, lentils or wheat) and then offered the choice of an alternative grain type (malt barley, durum wheat or lentils) for five nights. Mice displayed a strong preference towards cereal grains, with a slight preference towards malt barley (Table 1).

Table 1. The average proportion consumed by mice (expressed as a percentage %) of alternate malt barley, durum wheat or lentils compared to the back ground food type, after being on a background of lentils, barley or wheat for 2 weeks (n=10). Mice displayed a significant preference for cereal grains over lentils.

Experiment 2: Toxic bait take against different background grains

Experiment 2 is aimed at determining the acceptance of different toxic bait substrate by mice when challenged against different background food type. Mice were held on a background food type (lentils, barley or wheat) then offered an alternative of three types of zinc phosphide-coated grain for three consecutive nights as well as the background diet. Mice consumed toxic bait grains regardless of bait substrate type. However, background food type had a strong influence on the amount of toxic bait consumed (Table 2). Mice established on a wheat background consumed fewer toxic bait grains then mice on a lentil or barley background diet. Mice on a barley background diet showed a preference for malt barley.

Table 2. Average number of toxic bait grains consumed by mice that died held on either lentil, barley or wheat background.

Toxic bait aversion

Average toxic bait uptake was highest on the first night of exposure. Mice that did not die after consuming toxic grains showed a strong bait aversion (Table 3). By night three of the trial, baited mice stopped eating toxic grains.

Table 3. Number (average) of toxic bait grains consumed by mice that did not die in the lentil (n=4), barley (n=14) and wheat (n=16) background food types over the three-night trial.

Experiment 3: Effect of alternative food quantity on bait effectiveness

This trial will be undertaken in large enclosures and is designed to examine the role of available alternative food on commercial zinc phosphide bait effectiveness. The effect of commercially available zinc phosphide bait will be measured using four groups of mice provided with different levels of available background cereal grains (Table 4).

Table 4. Amount of food and bait to be applied to each treatment group in the Enclosure study

1. Mouse ecology

This work will involve a series of experiments aimed at understanding how mice use zero and no-till cropping systems. Historically, mice lived on the margins of paddocks and moved into crops when conditions were favourable. Now with low levels of disturbance in paddocks, mice are building burrow networks in paddocks and living where resources are most plentiful.

This project will address five key topics:

1. Farming practices.
2. Managing refuge habitat.
3. Understanding mouse movements.
4. Mouse burrows.
5. Bait delivery.

Understanding the impacts that farming practices have on the distribution of resources in paddocks and how mice access these resources and use the associated habitat will assist in the development of new strategies to control mice.

Monitoring outcomes

Ongoing monitoring of mice across all cropping regions is critical to provide accurate predictions of future populations of mice and in turn provide accurate information to growers about changes in mouse populations.

In the autumn of 2018, mouse numbers in the Victorian Mallee were extremely high and while numbers on the Adelaide Plains were not as high, there was still cause for concern (Figure 1). In general, growers were well prepared for mice in the lead up to sowing and significant quantities of bait were spread prior to and during the sowing of the 2018 crop. The combination of an extremely dry summer, and a dry and cold autumn and winter, in conjunction with the distribution of large amounts of bait led to a decline in mouse numbers in late May-early June and since then mouse numbers have remained low.

Figure 1. Current mouse population abundance at benchmark sites in Victoria and South Australia compared to outbreaks in the past.

Current research outcomes

The results from the bait substrate trial show that mice have a clear preference for cereals over lentils. While there appeared to be a slight preference for malted barley, there was no significant preference for any of the cereals.

When challenged with toxin on different cereal grains, mice were willing to eat the toxin regardless of the substrate, but background food significantly affected the number of toxic grains consumed. Mice that were on a background of lentils ate significantly more toxic grains than mice that were on cereal backgrounds.

Mice that ate a sub lethal dose of toxin on the first night showed bait aversion – they stopped taking toxic grains on nights two and three.

The next phase of this work aims to determine the effect of the amount of background food on the efficacy of zinc phosphide.

Future research

The results of the bait substrate experiments, in conjunction with the results of the work in the five key mouse ecology priority areas, will form the basis of a series of recommendations for improved mouse control strategies. The current approach to bait application is to spread bait on a broad scale across entire paddocks. To date, the majority of our understanding of mouse ecology and behaviour is based on work undertaken in conventional cropping systems. Better understanding of mouse ecology in zero and no till cropping systems could lead to more strategic application of bait, potentially reducing the quantity of bait spread or increasing the effectiveness of bait by targeting high activity zones in paddocks.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC – the authors would like to thank them for their continued support.

Contact details
Steve Henry
CSIRO Health & Biosecurity
GPO Box 1700, Canberra, ACT
02 6246088
Steve.Henry@csiro.au
@mousealert