Mouse plagues - Stored Grain

From: E.J. Wright, M.C. Webb and E. Highley, ed., Stored grain in Australia 2003.
Proceedings of the Australian Postharvest Technical Conference, Canberra,
25–27 June 2003. CSIRO Stored Grain Research Laboratory, Canberra.
Mouse plagues — when, where and why
Julianne Farrell
Department of Natural Resources and Environment, PO Box 318, Toowoomba, Queensland 4350
What causes a mouse plague?
Female mice reach sexual maturity at around 6 weeks of
age and are prolific breeders. Breeding begins in spring
and continues into autumn, given suitable weather conditions. The length of the breeding season is influenced by
food supply and seasonal conditions. An extended
breeding season can lead to a population explosion in
autumn, where up to 1400 mice per hectare have been
recorded on the Darling Downs in Queensland.
Considerable damage is caused to crops, grain storages, intensive livestock operations, buildings and
machinery at these high numbers.
feed storage losses and yield decline. Disease risks
increase because mice can transmit salmonella as well as
other pathogens that cause illness in livestock.
Grain growers also suffer damage to buildings,
machinery, vehicles, electrical wiring, phone cables and
insulation.
Mice impact on the environment during plagues by
depleting soil seed banks and reducing ground cover,
which can lead to increased soil erosion. Baits used to
control mice may cause non-target mortalities if not used
according to label directions.
Monitoring mouse numbers
How do mouse plagues end?
Monthly trapping surveys are undertaken at various sites
on the Downs and in central Queensland. Data collected
on body size, sex and breeding status are used to generate
predictive models. Plagues can often be predicted up to 6
months in advance and warnings are distributed through
the local media.
Monitoring at various sites in Queensland is undertaken
on a monthly basis by Department of Natural Resources
and Mines staff. Farmers are also encouraged to regularly
check their properties and crops for signs of mouse
activity, and take management actions that will reduce the
populations.
Monitoring methods include:
• trapping—snap-back and live-capture traps, which
allow for mark/recapture studies and microchipping or
radio-collaring individuals
• bait cards—introduced as a technique for estimating
the likely effectiveness of crop baiting
• visible sightings—the presence of active burrows or
pathways, and counting numbers seen at night can be
good indicator of mouse abundance
• crop damage assessments—counting damaged plants
per unit area
• rate of bait removal—the amount of bait removed from
around sheds or grain storages is a good indicator of
increasing or decreasing populations.
The impact of mouse plagues
Controlling mice
Mice cause the greatest economic impact by damaging
grain crops at all stages of growth as well as in postharvest
storage.
Intensive agricultural industries also suffer losses to
fruit and vegetable crops from direct damage and fouling
with excrement, damage to animal sheds and equipment,
The main method of control for mice in agricultural as
well as urban settings is with poison baits (rodenticides).
Integrated pest management (IPM) techniques—which
give more effective, long-term control—combine baiting
with trapping, habitat manipulation, reducing food availability and removing refuge habitat.
Most plagues end in July when food is becoming scarce
and cold winter conditions stress the population. At high
population densities, disease spreads rapidly and aggression increases, leading to wounds that become readily
infected.
Consequently, the mice are sick and hungry, making
them more susceptible to disease, infection and climatic
extremes.
When populations crash, they do so rapidly—over a
period of 2 days to 2 weeks.
Can mouse plagues be predicted?
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Mouse plagues — when, where and why
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Stored grain in Australia 2003
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Baiting—various rodenticides are registered for use
around buildings, storage facilities and in crops. They
are predominantly anticoagulants and should be used
according to label instructions to achieve maximum
effectiveness and reduce the incidence of non-target
kills.
Manipulating habitat—can delay population
increases by modifying breeding and feeding areas.
Grazing stubble after harvest will reduce the spilt
grain that is readily utilised by mice. Ploughing in
stubble and mulch may be advisable if mouse populations appear to be increasing. This reduces the cover
available that will increase the opportunities for predation, as well as burying any remaining seed
sources. Farmers should be aware of the increased
possibilities for erosion if stubble and mulch is incorporated.
Trapping—snap-back traps are an effective means of
controlling low numbers around houses and buildings. Water traps are another common method of
reducing numbers. Both methods are useful for monitoring mouse numbers over time.
Reducing food supply—clean grain spillages around
storage sites immediately, store grain away from paddocks, store bagged seed off the ground and avoid
hessian and paper packaging, and store produce in
mouse-proof facilities where possible. Buildings
5.
should have all holes and gaps in walls, doorways etc.
larger than 6 mm diameter blocked. Steel wool makes
an effective blocking material. Ensure doors fit well
and are kept closed.
Controlling refuge areas—wherever possible, eliminate grassy verges, weeds and rubbish dumps to
reduce mouse feeding and breeding areas. Slash or
burn fence-lines, roadside verges and irrigation channels.
Reference
Caughley, J. 1999. Controlling mice to prevent plagues. Queensland, Department of Primary Industries (DPI) Farming
Systems Institute CropLink. Agdex No. 672.
For more information, contact:
Julianne Farrell
Rodent Zoologist
Robert Wicks Pest Animal Research Centre
PO Box 318
Toowoomba, Queensland 4350
Phone 07 4688 1142
Fax
07 4688 1448
Email Julianne.Farrell@nrm.qld.gov.au
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