Mice activity increase in Pingrup and Esperance areas

While high grain prices are currently on offer for this season, record high input costs such as fuel and fertiliser are also adding to production risks.

With that in mind, growers will be taking whatever steps they can to minimise any potential losses, with controlling mice numbers high on the priority list.

For Pingrup farmer and WA Grains Group chairman Doug Smith, mouse numbers in the Lakes area are as bad as he's seen them the entire time he has been farming.

"Because last year was such a big harvest, there was a lot of grain that went out the back of headers and a lot of straw, so numbers built up very quickly," Mr Smith said.

"There are plenty of activity signs in the paddocks, lots of burrows and certainly enough numbers for it to be very concerning.

While he hasn't personally started baiting yet, there are plenty of farmers in the area who have had to get the process underway, with some soil types appearing to be worse than others.

"Because we're dry seeding and using a DBS, we are ripping the burrows when we're sowing and we're not sure how much that might have affected the mice populations in those paddocks," he said.

"We will do some monitoring and make a decision over whether we need to bait, but we have some on hand ready to go."

With seeding underway in most cropping regions, growers were being warned to monitor their paddocks closely for any signs of mice and remain vigilant during seeding and the growing season.

Chew cards cannot be relied upon while food sources are high and it is recommended growers monitor for active burrows at several sites to gain a true representation of population size.

Grain Producers Australia (GPA) special projects manager Andrew Weidemann said many growers had already started baiting, or are about to start their programs, in response to what's happening with mice activity in their own paddocks.

"As we saw with last year's mouse plague, a serious outbreak can significantly impact crop returns and the general wellbeing of our regional communities," Mr Weidemann said.

"That's why we need to remain vigilant with monitoring our paddocks and be proactive with control programs, to minimise mouse numbers and limit damage, as best we can."

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Mice cause damage at all stages of crop development but are most severe at sowing, for about two to three weeks after crop emergence and again at flowering/early seed-set.

For that reason, it is important that during seeding growers remain observant, keep monitoring burrow numbers and bait within 24 hours of sowing to protect seed if control is required.

Farmers and agronomists around the Esperance area have been aware for over three months that mice are likely to pose an issue this year.

While rodent activity may not be unheard of for the region, this year has been a perfect storm in that they are present in more areas, there was a big harvest last year with very little summer rain and now one of the best starts in years.

Farm and General agronomist Monica Field, who has been working in the area for eight years, said this was the worst she had ever seen the problem.

"The standard that we look for as a threshold is two holes in 100 metres, but I've seen areas where there's five or more and with that many there we are starting to look at plague numbers," Ms Field said.

"You can see on certain farms where there's been more losses at harvest that there's an increased burden, while farms that have used seed terminators or other destructor type products seem to be slightly better off."

Early-sown canola paddocks have been the main focus for Ms Field's clients, with a lot of paddocks baited directly after the seeder and the odd hectare having to be baited twice.

"They're building up in areas where farmers have not had problems before and in general as we're moving into cereals, we're watching numbers to see if they need to be baited," she said.

"There are areas on the western side of town where farmers have pretty much had to bait the whole farm and while there are numbers on the east, it's not quite to the same extent."

With numbers increasing, growers are hoping the weather will play its role with a good downpour needed to help control the problem.

"Depending on the conditions going forward, we could see a damage scenario similar to what's been experienced over east in recent years," Mr Smith said.

"In fact, the base numbers are already there at the moment, so without serious baiting and some weather conditions to go against the mice, we could see a really dire scenario."

With mouse activity on the rise, DPIRD recommended growers use 50 grams per kilogram zinc phosphide (ZP50) baits to ensure the best chance of success with their baiting programs.

The ZP50 option was provided to support growers with stronger crop protection options through an emergency use permit issued to GPA last year, which remains in place.

Zinc phosphide mouse baits are an S7 chemical so must only be sourced from licensed suppliers and manufacturers and are registered for in-crop use only, with strict baiting criteria having been established to minimise off-target impacts.

Growers should monitor paddocks post-baiting because if populations are high, mice may move back into the paddocks from adjacent, unbaited areas, normally within a week.

If any hot spots are discovered, those areas need to be re-baited with the existing zinc phosphide label allowing for re-baiting every two weeks if necessary.

Mr Smith said having previously only had the weaker ZP25 baits, the control from ZP50 was far superior.

"It is possible that the bait situation in WA will become dire because we need so many of them and there is not enough to cover the entire State," he said.

"With that in mind people will have to resort to using ZP25, but if farmers can access the ZP50 for critical paddocks, then they definitely should."

CRITICAL FOR MICE TO RECEIVE THE RIGHT DOSE

THE new mixing rate of ZnP-coated wheat bait was lethal in all mice while the previous bait mixing rate was only lethal in 50 per cent, according to a lab study by CSIRO and the Grains Research and Development Corporation (GRDC).

The new Australian Pesticides and Veterinary Medicines Authority (APVMA) emergency use permit increased the concentration of zinc phosphide active per wheat grain from 25 grams per kilogram to 50g/kg.

The bait will still be applied onfarm at one kilogram per hectare but will have twice as much ZnP on each grain, increasing the likelihood of a mouse consuming a lethal dose in a single feed.

CSIRO researcher Steve Henry, who led the study, said it was critical every grain of bait represented a lethal dose.

"Our lab research has shown that mice rapidly develop aversion to the bait, meaning that if they do not consume a lethal dose from one grain of bait, they will not consume any more toxic grain," Mr Henry said.

The increase in bait mixing concentration was well received by industry, especially with many growers across the country currently battling high mouse numbers ahead of winter crop planting.

GRDC pests manager Leigh Nelson said current farming practices conserved water and were environmentally sustainable, such as minimum or zero tillage, and had resulted in a significant increase in both available shelter and alternative food sources for mice.

"Mouse management requires an integrated approach and a key part of this is the reduction of alternative food sources, such as grain being left in the paddock post-harvest," Dr Nelson said.

"This residual grain greatly reduces the probability of a mouse encountering and consuming a treated grain.

"So even with the increased bait mixing concentration, growers will still need to ensure they implement best practice tactics on farm for effective mouse control."

The efficacy research from CSIRO and GRDC produced consistent, scientifically rigorous results and followed the Organisation for Economic Co-operation and Development (OECD) guidelines and was approved by a CSIRO Animal Ethics Committee.