Mouse plague prediction models relevant forecasts for growers in Queensland

GRDC code: IAC00002

Authors

Julianne Farrell, Consultant and Peter R. Brown, CSIRO Ecosystem Sciences

Background

The house mouse (Mus domesticus) is a serious pest to agriculture in Australia. Mouse populations occasionally undergo widespread eruptions (mouse plagues) in the grain-growing regions of Australia. On the central Darling Downs in the past, damaging mouse densities occur every 2 years and a plague every 4 years. Large parts of the grain-growing regions of south-eastern Queensland were hit by a mouse plague in 1995, but outbreaks have occurred also 1997, 2000, 2002 and more recently in a minor outbreak in 2010/2011. It is generally believed that dry conditions are needed before a mouse outbreak in Queensland, which is in contrast to the wet conditions needed for outbreaks in southern states (SA, Vic, southern NSW).

GRDC have funded a 3-year study to monitor mouse populations and forecast the likelihood of mouse outbreaks. The project is a collaboration between Landcare Research (New Zealand), CSIRO Ecosystem Sciences and the Invasive Animals Cooperative Research Centre. Mouse populations are monitored in typical grains farming systems in Western Australia, South Australia, Victoria, New South Wales and Queensland (Figure 1) at 3 key times each year. The monitoring provides data on the abundance and breeding status of mouse populations. This information is used in models that have been developed progressively over the last 20-30 years to predict mouse outbreaks.

Mouse monitoring

Currently, monitoring of mouse populations occurs at 3 levels of intensity across 11 sites:

1. Benchmark sites in the Adelaide Plains (SA), Northwest Victoria, and the central Darling Downs (Qld), where long-term trapping has been conducted (>20 years) and where forecast models have been developed. Live trapping data are collected at 3 key times a year and the data are used in the models to predict the likelihood of outbreaks for those regions.
2. Quantitative rapid-assessment sites in WA (Geraldton and Ravensthorpe), Victoria (Horsham and Walpeup), NSW (Riverina and Moree), SA (Roseworthy) and Queensland (Central Queensland and central Darling Downs) where there are two types of monitoring: mouse chew cards set out overnight (ten bait cards or canola squares at 10 m spacing along 100 m survey lines), and active burrow counts along 100 m survey lines. Monitoring is conducted 3 times a year.
3. Qualitative monitoring networks in all the areas with rapid-assessment sites plus Eyre Peninsula (SA) and Central West NSW where key farmers and agronomists are contacted to collect information about mouse activity in the region as well as any reports of the use of rodenticides.

Figure 1. Approximate locations of mouse monitoring occurring in WA, SA, Vic, NSW and Qld.

Current situation for the central Darling Downs, Queensland, and prediction of a mouse outbreak?

Mouse monitoring on a transect between Mt Tyson and Cecil Plains on the Darling Downs was conducted in September 2013 (spring) and December 2013 (summer). Trap results for September indicated that mice were present in higher numbers than usual for spring, and were causing damage to maturing wheat crops.

The December trap index was 9.5% trap success (Figure 2). The short-term model predicts that the March 2014 population index will be moderate and the May 2014 population index will be high. Most adult females were pregnant. Plague prediction modelling of this latest data confirms that mouse numbers are increasing, with a high population density index expected during the period leading up to May 2014. The next routine monitoring will occur in March 2014.

The practical implication of this prediction for grain growers on the Darling Downs is the potential for increased levels of mouse-related crop damage in maturing sorghum crops. GRDC suggests that growers should closely monitor their crops for mouse activity and damage in the lead up to harvest, and consider baiting with a zinc phosphide-based product to reduce damage to both summer and planned winter crops.

Because of the high variability observed in mouse abundance across the 32 km transect, it is necessary for farmers to monitor mouse activity themselves on their own properties and to make a decision about whether they should take preventative action such as baiting with zinc phosphide.

Growers are reminded that there is a two week withholding period for zinc phosphide baiting prior to harvest. Other mouse management activities that can be carried out include mowing/slashing fence line and roadside verges to reduce alternative shelter and food sources, and cleaning up grain spillages that occur during harvest.

Figure 2. Current monitoring of mouse populations in central Darling Downs QLD (December 2013) compared mouse abundance in the past.

Figure 2 text description
The following are approximates:

• Central Darling Downs in July 2013 had a trap success rate of 14%, decreasing to 3% in October, and increasing to a predicted high of 18% in May 2014.
• Callide in July 2013 had a trap success rate of 11%, decreasing to 8% in October, and predicting stable trap rates (minor increases and decreases) until May 2014.
• Dawson in July 2013 had a trap success rate of 6%, increasing to 9% in December, and predicting a minor increase to 10% in March 2014, followed by a decrease to 5% in May 2014.

Current situation in other areas

Recently completed monitoring of mice in the Dawson and Callide Valleys in central Queensland and around Moree in northern NSW shows mouse numbers are slightly up on what was seen during September, but that populations are not high enough to be causing economic damage to crops, or to justify the expense of baiting.

There is a chance that mouse abundance will be relatively high at sowing of winter cereal crops in the Eyre Peninsula and Yorke Peninsula, South Australia, and the central Darling Downs, Queensland. Mouse populations are low across all other locations where we have monitoring data. The forecasts are based on information about the abundance of mice and rainfall over the growing season of the winter cereal crops. The next routine monitoring will occur in March 2014.

Contact details

Peter R. Brown
CSIRO Ecosystem Sciences
Ph: 02 6246 408602 6246 4086
Fx: 02 6246 4000
Email: Peter.Brown@csiro.au

Julianne Farrell
Ph: 0411 257 8310411 257 831
Email: juliannefarrell17@gmail.com

Reviewed by

Steve Henry, CSIRO Ecosystem Sciences