Farm Management

Growers advised to prepare for potential mouse problem in spring

CSIRO researcher Steve Henry checks a trap on a property near Mallala on the Adelaide Plains during a recent round of surveying mouse activity for the GRDC monitoring program investment. Image supplied by GRDC

Grain growers in Victoria and South Australia should be prepared for a potential issue with mice in spring 2017.

The latest reports from the Grains Research and Development Corporation’s (GRDC) regular mouse monitoring program investment indicate that mouse populations remain at moderate levels in grain-growing regions across both States.

While mouse numbers are expected to decline over the remainder of winter, particularly if conditions are cold and wet, there is concern amongst scientists monitoring the situation that the sizeable background population and potential stored food reserves will enable a rapid increase in numbers when breeding recommences in spring.

To prepare for such a potential scenario, growers are being advised by the GRDC-supported National Mouse Management Working Group to continue actively monitoring mouse activity and look for signs of mouse damage, such as chewed tillers and nodes.

If mouse populations are high (more than 200 mice/hectare, when they cause economic damage), growers should consider baiting now before crops flower, as flowering crops are highly vulnerable to damage from mice.

If mouse populations are low (10-20 mice/ha) to moderate (50-100 mice/ha), growers should remain vigilant until the start of spring.

Trapping in June 2017 near Mallala in SA revealed densities of 30-50 mice/ha, and at Walpeup in Victoria densities were 30-60 mice/ha.

Growers are encouraged to communicate with their local bait supplier to be informed of supply timeframes and to determine whether pre-purchasing of bait is required. Crops cannot be treated with bait within 14 days of commencement of harvesting.

CSIRO researcher Steve Henry, who has just completed another round of surveying mouse activity for the GRDC investment, says vigilance  is critical as crops cannot compensate for heavy damage should it occur.

“If numbers build up significantly over spring, crops could be at serious risk of damage and the problem could continue after harvest and ahead of sowing 2018’s crops,” Mr Henry says.

“Even if growers don’t think they have a mouse problem, they should continue to monitor for activity through winter.”

He recommends growers look for evidence of active burrows: “I suggest farmers walk about 30 metres in from the edge of the paddock and set a 100 metre (1 metre wide) transect through a crop, following the furrows.

“They should walk slowly along the transect scanning for evidence of mouse burrows, taking note of any burrow that looks active and recording the number of burrows per 100 metre transect, and then repeat across two or four transects.

“If there are more than two to three active burrows per 100 metres, then they have a mouse problem.”

Mr Henry says corn flour can be used to mark potentially active burrows, but the transect will need to be inspected the next day for observation of signs of activity.

  • In terms of zinc phosphide baiting, Mr Henry recommends the following:
    Apply bait according to the label;
  • Allow at least four to six weeks before re-application of baits to minimise the chance of bait aversion. This allows mice that have previously tried the bait to try it again and also targets new animals in the population that are susceptible to the bait;
  • Bait over large areas. Encourage neighbours to bait at the same time if they also have a mouse problem. The larger the area treated, the lower the chance of re-invasion post treatment.

Mr Henry’s recent survey took in areas such as the northern Mallee and Wimmera in Victoria, and the Mallee, Adelaide Plains and Yorke Peninsula in SA.

He says paddocks supporting heavy stubble loads, particularly barley, as a result of 2016’s bumper harvest were most notably affected by mice as they offered ideal habitat.

“Some farmers have been hammered by mice in 2017, while others have experienced little or no issues. It has been a highly variable situation, and that has even applied from one paddock to the next on some properties.”

Mr Henry encourages growers and advisers to report and map mouse presence, absence and level of activity using MouseAlert so others can see the scale and extent of localised mouse activity.

MouseAlert also provides access to fact sheets about mouse control and forecasts of the likelihood for future high levels of mouse activity in each grain-growing region.

The next round of monitoring is in mid-September 2017 to coincide with the start of breeding and to inform industry about likely damage.

Meanwhile, the GRDC is proactively investing in research and development so that growers will have new management tools and strategies for mouse management in the future.

The current GRDC mouse monitoring investment is a collaborative project involving CSIRO Agriculture and Food, and the Centre for Invasive Species Solutions.

Source: GRDC

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