WithTheGrain: Reduce feed sources to control mice over summer

Author: | Date: 11 Jan 2018

Summer spraying provides an ideal opportunity for growers to monitor mouse numbers from a height, but getting out of the tractor or ute and closely monitoring burrow activity is required to understand the complete picture.

CSIRO research officer Steve Henry says 2017 conditions were ideal for mice numbers to flourish and extra diligence would be required across the southern region heading into the pre-seeding phase.

“There have been a whole range of things going on that lead us to be concerned about mice numbers, particularly on the Yorke Peninsula in South Australia and in the Wimmera and Mallee regions in Victoria,” he says.

“There was quite a bit of frost damage across Victoria in early November which has resulted in a lot of dead grain heads on the ground. On the Yorke Peninsula, desiccated lentil crops were hit by a windstorm. There were other isolated weather events which have caused issues locally.

“All of these events cause more food to be available to mice on the ground.

“We had already started the 2017 spring with a higher than normal number of mice, which occurred following the large harvest from 2016 where available grain from spillage and screenings encouraged population growth.”

Mr Henry says the key factor influencing mice numbers over the summer period was the amount of available food. He says growers need to be vigilant in keeping paddocks as clean as possible to keep numbers down.

“Our key recommendation for growers at this time of year, while they’re cleaning up after harvest and getting ready for sowing, is to reduce the amount of food available to mice,” he says.

“Every weed and volunteer germination should be sprayed. If there are sheep in the rotation, graze the stubbles. Not only will sheep eat the grain, they’ll also bury some of the grain, which allows it to germinate in the next rainfall and be sprayed out. It also means the mice have to dig for their food, making it that much harder.”

 

Mouse

CSIRO research officer Steve Henry says 2017 conditions were ideal for mice numbers to flourish and extra diligence would be required across the southern region heading into the pre-seeding phase.

Mr Henry says indicators of mouse numbers increasing include numerous burrows or fresh activity, large numbers of mice seen at night either in paddocks or on roads, signs of seed being dug up, plants being chewed or pod and head damage, frequent daytime sightings and more birds of prey than normal.

“The difficulty with the avian predators is that they’re not able to regulate increasing mouse populations,” he says.

“If mice are there in a normal season, then there is downward regulation of the mice. But once conditions get favourable for mice to increase, there’s no chance for the downward regulation as the predators can’t keep up with the pace of the mice breeding.”

Active burrow counts

The most effective way for growers to monitor the mouse population on their own property is to carry out an active burrow count.

  • Walk about 30 metres in from the edge of the paddock.
  • Set a 100m by 1m wide transect through the crop/stubble following the furrows.
  • Walk slowly along the transect scanning for evidence of active mouse burrows. Corn flour can be placed near potentially active burrows and checked the following day for evidence of fresh tracks or disturbed soil.
  • Be strict about keeping within the 1m transect. “For every additional burrow you add into a 1m squared section, you can skew your data to add up to 100 extra burrows per hectare,” Mr Henry says.
  • Record the number of active burrows per 100m transect.
  • Repeat across 2 or 4 transects to cover a large area.
  • If there are more than 2-3 active burrows per 100m, there is a mouse problem.

Knowing when to bait

Mr Henry says mouse chew cards, which are set overnight and the proportion of the card that has been chewed is recorded the following day, provide a good indication of mouse presence but results can be skewed when there were alternative food sources available as mice are less likely to mark the cards.

Similarly, he says baits are most effective when there is limited alternative food as the probability of the mice taking the bait increases with the absence of additional food options.

“If all the food sources and have been removed and other methods have been tried, such as rolling stubble to make the mice more visible to avian predators, and there are still high mouse numbers then growers can consider baiting in late summer, around February/March,” Mr Henry says.

Mr Henry advises growers to adhere to label rates when applying baits and apply baits at least six weeks prior to sowing.

GRDC research codes: IAC00002

More information

Steve Henry, CSIRO
0428 633 844
steve.henry@csiro.au

Useful resources

GRDC Tips & Tactics: Better Mouse Management

Mouse Alert website

GRDC Project code: IAC00002