Mice threat to no-till prompts new research push

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Key points

Photo of CSIRO researcher Steve Henry weighing a mouse

CSIRO researcher Steve Henry weighing a mouse trapped at Walpeup, Victoria, in September 2017.

PHOTO: Peter Brown, CSIRO

  • The GRDC has announced investments of more than $4.1 million into new mouse control research, development and extension initiative.
  • The new initiatives build on previous GRDC investments into mouse control of more than $70 million over the past 20 years.
  • $3.25 million will be invested over five years to better understand mouse ecology, biology and management in minimum tillage and stubble retained farming systems.
  • $630,000 will expand CSIRO’s national mouse-monitoring and surveillance program to better predict mouse outbreaks.
  • $275,000 will be invested to explore mouse feeding preferences and bait efficacy.
  • In the meantime, growers in areas where mouse numbers were high in the lead up to sowing are encouraged to apply zinc phosphide bait according to the label rate of one kilogram per hectare at seeding or within 24 hours of planting paddocks to crops.
  • Report observations via MouseAlert to assist other growers.

With escalating mice numbers poised to wreak havoc on crops in many areas, the GRDC has announced a further $4.1 million in new mouse control research, development and extension initiatives. In the meantime, experts are urging correct baiting procedures where mouse numbers have been high in autumn.

Map graphic showing mouse abundance at March 2018

Figure 1 Current mouse abundance (March 2018).


Australia’s largest single investment into mouse-related research was announced by the GRDC during a national webinar involving mouse control experts and growers in late March.

During the webinar, GRDC managing director Dr Steve Jefferies said more than $4.1 million would be allocated to mouse control research, development and extension (RD&E) initiatives in response to a build-up of mouse numbers in Australian farming systems.

Dr Jefferies said the GRDC recognised the enormity of the mouse problem (Figures 1 and 2) and the distressing impact it had on grain businesses, families and communities.

He said CSIRO would lead three new projects that would attempt to understand why mouse numbers seemed to be remaining high, rather than cyclical, and develop new and more effective control methods.

Graphic showing mouse numbers now

Figure 2 Mouse numbers now.


Ecology and biology

With the first investment – $3.26 million over five years – CSIRO-led research will seek to better understand the behaviour of mice under no-tillage and stubble retention systems to quantify the impact of various management tactics (such as strategic tillage, different seeding systems, food and habitat reduction) on mouse numbers.

Previously, management strategies to control mice were based on research conducted in conventional cropping systems, which often incorporated tillage, burning and removing stubbles, as well as grazing.

Dr Jefferies said farming systems had changed significantly since the previous research was done, with no-tillage, stubble retention and no livestock now the norm on many farms.

“We need to know whether conservation farming practices are favouring the persistence of mouse populations from one season to the next due to the maintenance of year-round habitat, a lack of soil disturbance, or whether there are also other factors at play,” he said.

“We are no longer seeing a plague situation one year, followed by a crash in the mice population and the absence of mice for extended periods thereafter.”

These days, Dr Jefferies said, mice seem to be a constant presence, with high-yielding crops and heavy stubbles appearing to provide abundant food and protection.

Technologies such as in-burrow cameras and radio-tracking devices are planned for use during the research to better understand mouse behaviour.

Mouse monitoring is critical

A second GRDC investment, of $630,000, will broaden and extend CSIRO’s existing national mouse-monitoring and surveillance program to better predict possible mouse outbreaks and protect crops. Dr Jefferies said the planned new program aimed to offer precise and real-time warnings of potential mouse plagues.

Feed preferences and bait

The third new project will see the GRDC invest $275,000 to investigate mouse feeding preferences and bait efficacy.

Dr Jefferies said the broadscale application of zinc phosphide to wheat grain, or bait at a rate of one kilogram a hectare, was currently the only method available for controlling mice in broadacre crops.

He said the efficacy of this bait had become an issue and this investment would explore the conditions that had led mice to finding zinc phosphide bait less attractive.

Dr Jefferies also said researchers wanted to answer two questions: the role of background food availability on baiting efficacy, and whether there were more suitable bait substrates.

“It appears mice have an aversion to wheat-based bait in some situations, which could be due to having access to more attractive food sources on the ground, like pulses,” he said.

The research would also investigate if mice were stockpiling food sources that were not baited and if they were using this as a survival technique to avoid taking the bait.

National Mouse Management Working Group chair Ian Hastings, who farms near Ouyen in north-west Victoria, welcomed the GRDC’s new mouse research investments: “The issues that will be looked at are issues that have come through the National Mouse Management Working Group and it’s pleasing to see the GRDC have come on board to solve some of the problems we’ve been talking about,” he said.

Control options

CSIRO’s Dr Peter Brown told webinar participants that reducing the food supply for mice was an important part of any integrated mouse management plan.

“Burning stubble or light tillage with a prickle chain were options,” he said. “Reducing the amount of cover increases the predation risk for mice, which is likely to improve the chance of mice taking bait spread at sowing.” In the Mallee region, Mr Hastings said, growers were cautious about using prickle chains because of soil erosion risks. He said growers in his area saw livestock as the best way to eliminate grain and other food sources from paddocks.

“At this stage I suggest the best method to control mice in our situation is to wait until we’ve run the seeder over the paddock and then bait within 24 hours.”

If possible, fit the mouse-bait spreader on the back of the seeder to apply bait at sowing, Mr Hastings said.

Feedback from growers in the webinar highlighted the complexity of the issue. For example, at Mallala, in South Australia, 60 kilometres north of Adelaide, grain grower Paul Lush said fitting a Harrington Seed Destructor to his harvester had done nothing
to diminish mouse numbers on his farm.

“Even where we were diligent in reducing our harvest losses, eradicating the food supply and eliminating the amount of grain on the ground, we’re still seeing alarming numbers of mice,” he said.

“I suspect the mice have been living on ryegrass seeds and the small amount of residue we’ve left behind in our full stubble retention, stripper front, single-disc seeder operation.”

Bait spreader modifications

Photo of mouse damage in a crop at Walpeup

Mouse damage in a crop at Walpeup, Victoria, in September 2017

PHOTO: Peter Brown, CSIRO

Growers have modified a variety of farm machinery to apply the one kilogram per hectare of zinc phosphide required to control mice present in their paddocks.

Two examples highlighted by Kondinin Group research manager and agricultural engineer Ben White (Seeder-mounted mouse bait spreaders) and Grain Central’s Neil Lyon (Farm-built baiting innovations take on mouse epidemic) include Victorian grower Brad Plant and New South Wales grower Michael Pfitzner.

Brad, who farms at Manangatang, Victoria, built a mouse-bait spreader that is ground-driven via his air-seeder cart, with a keyless drill chuck and drill bits used to modify the application rate. Product is metered into the air-stream and blown out to a swath width of about 16 metres.

Michael, who farms near Griffith, NSW, adapted a ‘whale-tail’ spreader, with bait product metered from the air commodity cart and drawn into a fabricated plenum mount for the whale-tail, which draws product in a Venturi style.

More grower innovations can be found by searching ‘bait spreader’ on Twitter.

Mice food supply

CSIRO scientific officer Steve Henry said he was not surprised mice were persisting from season to season, given the shift to conservation farming.

“One mouse only needs three grams of food a day to survive so it doesn’t take a heck of a lot of food to sustain a reasonable population of mice,” he explained.

“Some paddocks have significant numbers of ryegrass seeds per square metre on the ground, others have 20,000 brome grass seeds per square metre and this adds up when grain is lost from the front of the header.”

Mr Henry said reducing the available food on the paddock would increase bait efficacy: “If you turn over the top of the paddock using light tillage with a prickle chain, you destroy the food supply on the paddock surface and set the paddock back to zero.”

He said this could be checked by heading back to the paddock to see how many mice were breaking out of burrows and measuring mouse activity with mouse chew cards (with this issue of GroundCover™) and targeting them with zinc phosphide bait.

Mr Henry acknowledged that reintroducing tillage was a “huge decision to make”.

But he said mouse populations could be highly variable between paddocks and it was important to monitor for active burrows and to use chew cards to provide an indication of mouse numbers.

“Reporting your observations via MouseAlert can also help to provide observations for other growers in your region,” Mr Henry said.

Tillage impacts

Mixed farmer and GRDC Southern Panel member Richard Murdoch, who farms at Warooka on SA’s Yorke Peninsula, said some growers in his area had turned to tillage where mice were avoiding zinc phosphide bait. “Some growers are fitting a prickle chain to the rear of their seeders to stop mice from moving along a row and removing the seeds,” he said. “But people need to be aware of the potential for crop damage if using prickle chains immediately after sowing.”

Mouse control alternatives

Growers participating in the webinar wanted to know how long it would be before new mouse control alternatives would become available.

GRDC senior manager crop protection Dr Ken Young said past GRDC investments had already looked at a wide range of alternative active ingredients: “Most actives have been counted out because they are less efficacious, too expensive to apply or because they are toxic to non-target species such as birds, native fauna and humans,” he said.

“Over the past eight years we’ve narrowed down our pool of active ingredient alternatives and there is now only one on our list, which is in early toxicological tests in the US.”

Dr Young said it could be eight to 12 years before any new product became available.

One question raised in the webinar was whether mouse bait could be applied with snail bait – a practice Mr Henry strongly warned against.

“If you spread mouse bait and snail bait at the same time and it is equally distributed across the paddock, a mouse has an equal opportunity to take the snail bait as it does to take the mouse bait,” he explained.

“If a mouse takes a snail bait and all it gets is a belly ache, the chance of it eating any other novel food (mouse bait) that you have introduced to the system becomes very low.”

He said it was important that mouse bait was applied for one to two weeks before snail bait was applied to ensure mice take the intended bait.

Area-wide management

Dr Brown encouraged growers to think about an area-wide management plan based on a coordinated control effort among neighbouring farms.

This should provide plenty of bait across a wide area: “If the zinc-phosphide-treated grain goes out at two or three grains per square metre that’s the equivalent of 20,000 to 30,000 lethal doses per hectare,” he said.

Mouse plagues typically consist of 800 to 1000 mice per hectare, so there should be plenty of bait available – about 10 grain baits per mouse.

Mr Hastings said one of the strategies he used to manage mice after the initial zinc-phosphide application was a subsequent application around the borders of paddocks or near tree-lined ridges.

Mr Lush agreed with the need to protect paddock boundaries, saying sections of his 2017 crop disappeared in two days when mice migrated from adjacent burnt paddocks into his paddocks.

“Within two or three days of our initial baiting we had to re-bait and, in some cases, the mice nearly wiped out strips of crops because they just moved from one paddock to the next,” he said.

Mr Hastings said a blanket baiting was the ideal strategy where mice numbers were high, followed by strategic border baiting (keeping mindful of label specifications covering this) to prevent re-infestation from remnant vegetation or adjacent paddocks.

As the coming season progresses, Mr Henry said mice activity needed to be monitored over winter and spring.

“In a ‘normal year’, mouse numbers should decline in winter to almost undetectable levels in crops,” Mr Henry said.

But if numbers do rise in early spring, he recommended applying bait to avoid damage to the growing points of crops and developing heads.

More information:

Steve Henry
02 6246 4088
@MouseAlert (Twitter)

Useful resources:

Tips and Tactics: Better mouse management

Monitoring mice in Australia Update paper

Ag Excellence Alliance Controlling mice – Baiting strategies

Ag Excellence Alliance Mice control – a challenge for conservation farming

GRDC mouse control information

Mouse chew cards

A pad of GRDC mouse chew cards is included with this issue of GroundCover™. GRDC mouse chew cards can be downloaded from the GRDC website and printed. Additional mouse chew cards are available through GroundCover™ Direct, growers can place an order on freephone 1800 11 00 44 – copies of the pads will be free (no postage and handling charge).