Mouse Plagues: WHAT ARE WE IN FOR? 2011 and beyond

1. Mouse Plagues: WHAT ARE WE IN FOR?2011 and beyond • Greg Mutze • NRM Biosecurity

2. Mouse plagues Breeding patterns of mice in the mallee • Underlying reproductive biology • mice are primarily granivorous • low moisture requirements • no specific physiological or environmental cues • can produce a litter of 4-12 (avg. 6) every 3-6 wks • breed continuously when adequate food and cover available • Mice usually breed from October to March/April, depending mainly on food availability • start when seed from annual grasses and crops matures in spring • stop in autumn when seed supply declines - consumption, germination and spoilage • can start early if there is good rainfall in early autumn, which advances germination and seed-set from September to as early as June (e.g. 1983, leading to the 1984 mouse plague) • can be extended by November and summer rainfall, which damages mature crops and promotes summer weeds (e.g. 1992, leading to the 1993 mouse plague) • The mice that cause damage in population peaks during late autumn to winter were almost all born between October and April 24 mice from 1 hole at Kimba photo - L. Staples

3. Mouse plagues Development of mouse plagues • Population size is usually limited by: • low survival during winter, • length of the breeding season and • low breeding success and juvenile survival in cereal paddocks during extreme summer heat • During mouse plagues population increase is rapid and continuous from early spring to autumn

4. Mouse plagues Decline of mouse plagues Timing of plague decline • mouse numbers usually crash during winter, but • high numbers sometimes persist into spring • has major impact on the type of damage that occurs the 2 crop stages most prone to mouse damage: Damage only at seeding Damage at flowering

5. Mouse plagues historical perspective • Mouse plagues have occurred since cropping began in SA • every 5-6 years • Usually follow good cropping years, particularly with heavy early- or late-season rains • Damage crops planted in the same fields the following year • Increased frequency in the last 30 years • Plagues every 4 years • Severe plagues in 1980, 1993, 2010 • Significant damage in several other years, including 1996, 1998, 2002, 2004, 2006 • Similar trends elsewhere in Australia Data G. Singleton

6. Mouse plagues how has it changed • Increased frequency due to changes in cropping practices • conservation farming: less cultivation, stubble retention, new diverse crop types, new crop varieties, tighter rotations (more frequent cropping) • fewer livestock , summer legume pastures • Provides mice more food, better cover and undisturbed burrows • Mouse plagues in the past 30 years are also • affecting crop stages that have historically had few problems (e.g. tillering wheat) • affecting new crop types in traditional areas (e.g. lupins, canola) • affecting new areas (e.g. Mid North and Kangaroo Island) Mouse damage to wheat tillers Mouse damage to canola seedlings

7. Mouse plagues how has it changed The end result of these changes is: • More mice are likely for any given seasonal conditions • More damage to crops is likely for a given number of mice • Reduced tillage delays the timing of population decline until after crops are sown • Greater variety of crops gives a prolonged period of crops at vulnerable stages Mouse damage to wheat tillers Mouse damage to canola seedlings

8. Mouse plagues controlling damage in crops • Before 1996 • no registered products were available for mouse control in crops • unregistered chemicals were at times illegally used for mouse control • demonstrated ineffective for those tested: methiocarb and chlorpyrifos • risk of residue problems, because of uncontrolled mixing and application rates • severe off-target poisoning due to residual effects in scavengers that feed on mouse carcases (including hawks , kites, corvids & owls). • Strychnine • First used under permit in 1980 & 1984 • Widespread baiting program in crops in 1993. Bait was prepared by State and local government bodies and supplied at cost of production • Economical. Highly effective. • Strychnine is considered inhumane. International image is poor & not widely used. • not used after 1996 due to concerns expressed by our major international trading partners. • Still registered for use in sheds & storages (Dynamice®) but not in crops

9. Mouse plagues controlling damage in crops • Crop damage can be controlled by applying wheat-based grain baits • Registered zinc phosphide poison baits, commercially manufactured by 2 private companies • Applied to crops by landholders or commercial operators, from ground or air • Highly successful in baiting trials (~98% control) • When and where • Spread in crop paddocks before or after sowing to control damage to seed grain • Can be used in established crops to control damage at flowering stage (Sep-Oct) • Environmental safety • No residue problems (zinc and phosphorus are both mineral nutrients used by growing crops) • Limited off-target poisoning hazards (some common pigeons and parrots, few hawks or owls) • Costs in 2010 • Cost: $10-$15/ha, adds about 20% to cost of establishing a crop • Efficacy: multiple applications were necessary to control highest mouse densities

10. Mouse plagues landholder survey in 2010 • Survey of crop management factors affecting mouse damage in 2010 1 2 3 4 2 worst affected and 2 least affected crops on the same farm paddock history from previous 2 years paddock management in summer and at seeding Mouse baiting and damage at crop establishment

11. Mouse plagues Preliminary indications from EP growers • Mouse numbers higher where: • last year’s grain yields were exceptionally high • hail damage dropped maturing heads • more grain was spilled at harvest • on lighter or stony soils vs. heavier soils • on ungrazed vs. grazed stubbles or grassy pastures • adjacent verge areas with heavy nut-grass or spear-grass cover • Mouse damage at sowing was reduced by: • effective summer weed control (especially melons) • knocking down stubbles in summer (rolling, slashing, prickle-chaining or burning) • incorporating stubbles before or at sowing (cultivation or disc chains) • baiting at or immediately after sowing (vs. a few days to a week later) • early sowing (especially dry-sown crops, but they were badly damaged in previous plagues) • increased sowing depth (4-6 cm vs. 1-3 cm) • Multiple baiting was the only reliable strategy in the worst areas Melon seeds allow mice to persist in sown crops

12. Mouse plagues Preliminary data from survey • Yield losses in crop establishment were estimated as: • 30 % in worst affected crops (most of these had been baited, many only after damage commenced) • 6 % in least affected crops (on the same properties, most not baited) • Grain loss at harvest in 2009 was generally considered to have been low even in the crops that were worst affected in winter 2010 • Mouse populations in worst affected crops are thought to have been 500-1000 mice/ha • A mouse population reaching only 500/ha in June eats 140 kg seed/ha between January-June • Grain is also lost to insects, birds, livestock, germination etc • low recognition of harvest losses in bumper crops, and the consequences, may be a significant issue

13. Mouse plagues what is the current situation in 2011? • Potential for major problems at seeding • Good yields across most of SA last year • Difficult harvest conditions and high harvest losses • High carryover from 2009/10. Numerous reports of high activity in stubbles already • Summer rains have germinated much of the spilled grain, but might provide a source of fresh grain and summer weed seed during autumn • Similar reports are widespread in eastern Australia • Management options • Knock down stubbles early (in conflict with erosion control) • Graze hard and early (in conflict with erosion control) • Control summer weed seed-set • Bait at seeding • The future - new strategies to limit the quantity of seed left in stubbles