Mouse numbers build ominously

Mice numbers are building to worrying levels in parts of South Australia and Victoria.
Mice numbers are building to worrying levels in parts of South Australia and Victoria.

MOUSE numbers are building ominously leading into the 2017 winter cropping season in Australia, with authorities reporting that South Australia, Victoria and New South Wales are likely to see mouse damage in parts.

Simon Humphrys, of the Invasive Animals Co-operative Research Centre (CRC), said the team behind the Mouse Alert program had been baiting throughout autumn and had found an increased abundance of mice in several regions.

Numbers of mice are already at very high levels in key grain producing areas such as the Adelaide Plains in South Australia, where baiting at Mallala had a 75 per cent success rate, which is in the very high range.

Numbers are estimated at 250-320 mice per hectare, with Mr Humphrys saying any burden over 200 mice a hectare was likely to result in economic damage.

Numbers are well below the official definition of a mouse plague, which is numbers greater than 800 mice per hectare, but are still climbing.

Mr Humphrys said farmers with high mouse numbers would need to look at baiting.

Agronomists estimate the cost of the registered rodenticide zinc phosphide at between $7 and $9 a hectare.

Unlike in other years with high mouse burdens, estimates are that there are good levels of zinc phosphide stocks in store leading into planting.

Mr Humphrys said at this stage the Mouse Alert team expected significant damage at sowing in SA and parts of Victoria without baiting.

“Because of the bumper harvest last year, there is ample food and cover on most sites we are monitoring, particularly in cereal stubbles,” he said.

The mild summer in those parts is also expected to have allowed mice to continue to breed up.

Mr Humphrys urged growers to conduct their own monitoring to look for mouse activity when making decisions about whether to bait, such as evidence of active mouse burrows.

In SA, he said problem areas were likely to include the Adelaide Plains and the Yorke and Eyre Peninsulas.

Through Victoria, numbers are not as high as in South Australia for the most part, but are on the increase and are now at levels where some damage is possible, particularly in the Mallee and Wimmera.

The official Mouse Alert monitoring suggests a mouse outbreak is now highly likely through parts of Victoria.

The focus in NSW will be on the Riverina, where numbers are increasing in places such as Coleambally, while there is virtually no mouse activity in either Queensland or Western Australia.

In terms of baiting, the official instructions are to bait as early prior to sowing as practical to get the best possible control and then reassess whether rebaiting is necessary closer to planting.

Farmers are also encouraged to bait over large areas and to work together with neighbours to lower the risk of reinvasion.

Spread at label rates of 1kg/ha, Mr Humphrys said zinc phosphie should reduce mouse numbers by 95pc.

The Mouse Alert project operates nationally and collates data from a range of trial sites across the country.

Farmers are encouraged to report any mouse activity to the team through the website www.mousealert.org.au