After a bad year with mice in 2022, Bolgart, Western Australia, grower Trevor Syme explored several different mouse baiting strategies. Season 2022 was the first time Trevor had experienced mouse issues so a baiting program was implemented using his three-point linkage Amazone ZA-TS fertiliser spreader on cereal crops. Canola and lupins were subsequently baited as soon as they started to pod using a local aerial contractor.

Trevor Syme uses a Lehner SuperVario® 12V unit mounted to the rear of his BOSS® air seeder cart, but has experienced issues with the bait bridging in the gravity-fed unit. Photo: Ben White

Using a ZP50 bait, Trevor was able to achieve the required rate of one kilogram per hectare through manual calibration of the spreader. Although the unit has a self-calibration function, it was unable to handle the low rate.

However, issues were experienced with the quality of mouse bait used. “Some of the mouse bait we used had half heads, chaff and even corn, just all sorts of stuff in there. The spreader door is not open very wide, so it was blocking up or altering the application rate,” Trevor said.

Trevor initially targeted a spreader width of 48 metres but had to cut it back to 36m to achieve the 1kg/ha rate, which seemed to work well. But applying bait with the linkage spreader was an additional operation that Trevor wanted to avoid, so a Lehner SuperVario® spreader was purchased in preparation for seeding in 2023 and mounted to the rear of the BOSS® air cart.

The 12-volt unit features a 170-litre hopper and is gravity-fed to the spinner.

Seeding at 10 to 11 kilometres per hour at a 12.2m width, the rate from the bait spreader was successfully adjusted to 1kg/ha, but problems were soon encountered with bridging. “It would work fine until it would bridge. And then, because the agitator inside spins with the spinner, it was going too fast and just mulching the bait up,” Trevor explained.

“You don’t really know that’s occurring until you stop and have a look. The unit is at the rear of the tow-behind cart and you can’t see it from the tractor. And the rate is so slow sometimes it’s hard to tell if anything is coming out.”

The current system was used for Trevor’s 2023 canola and lupins program. While the unit has its limitations, there are no plans to change it at this stage and it will also be used for slug pellets. Trevor said a metered unit would probably have solved many of the problems experienced.

Harvesting a lodged barley crop in 2021 created alternate rows of long and short stubble. Trevor Syme believes the poor emergence of his 2022 canola crop in the long straw (far left) is directly related to the favourable mouse environment it created, compared with the short straw height (left). Photos: Trevor Syme

Residue management creates issues

Trevor believed the bad mouse issues experienced in 2022 were directly related to the use of chaff decks on the harvester in 2021. Decks were no longer used after this, with weed seed mills implemented in 2022. “We’re not grazing at all, and so all the grain and chaff is in a little line, like a buffet for mice.”

Mouse numbers have not returned to 2022 levels. Trevor also spent a fair amount of time minimising harvest losses to avoid leaving a food source. He also tried to process as much stubble as possible at harvest.

Trevor made an interesting observation with mouse damage to his 2022 canola crop, which was sown directly into barley straw. The previous year’s harvest was difficult due to the crop lodging, and successive passes with the harvester cut the straw alternately long then short due to the opposite travel directions.

“There was a full stand of canola every second pass where the straw was short, and where it was long straw there was no canola. I’m confident this was purely due to mouse activity, as the long straw gave them shade and provided a much safer habitat than the stuff that was cut at beer can height.”

Trevor also made the point that mice tended to prefer any freshly ameliorated ground as they could dig burrows far more easily. This was particularly noticeable due to the lack of burrows on the wheel tracks. “It’s like we create one habitat above ground with the long straw, and then another below ground with the easy digging.”

Mouse baiting for grain growers

Mouse baiting for grain growers

Mouse populations remain a significant challenge for grain growers across Australia and effective mouse management requires the precise and efficient application of bait.

The best results are achieved when combined with integrated pest management strategies. A recently published report – Mouse baiting for grain growers: Baiting equipment, guidelines and case studies – brings together the latest research and practical recommendations on bait spreading and machinery performance.

It also features case studies, such as this one from WA. Collated nationally, they report grower experiences regarding mouse control over numerous years up to December 2023.

Resources: GRDC – Mouse Management.