A Severe Rodent Outbreak Threatens Grain Production Across Western and South Australia

Australia's grain-growing regions are once again confronting a formidable challenge as mouse populations surge to plague proportions in parts of Western Australia and South Australia. Farmers report densities reaching thousands of rodents per hectare, devouring newly sown seeds, stripping emerging crops, and invading homes, vehicles, sheds, and even school grounds. The situation has forced many growers to spend hundreds of thousands of dollars on baiting programs and crop replanting, adding pressure to an industry already navigating global supply chain disruptions.

The outbreak began building in February under favourable breeding conditions, with numbers exploding rapidly in key cropping zones. In the worst-affected areas around Geraldton, Merredin, and Esperance in Western Australia, as well as the Adelaide Plains and Yorke Peninsula in South Australia, monitoring shows activity far exceeding the plague threshold of 800 mice per hectare. Estimates in some paddocks reach 6,000 to 10,000 mice per hectare, making traditional counting impossible and forcing reliance on burrow assessments instead.

Understanding Mouse Plagues in the Australian Context

Mouse plagues represent a recurring natural phenomenon in Australia's grain belts, typically occurring every four to five years when environmental conditions align for rapid population growth. The house mouse, introduced to the continent, thrives in the no-till cropping systems common across the wheatbelt, where abundant food sources from grain stubble and stored produce support explosive breeding. A single female can produce multiple litters in quick succession under mild temperatures and adequate moisture, leading to exponential increases within months.

These events differ markedly from typical rodent issues in urban settings. In rural Australia, the sheer scale transforms everyday farming operations into battles for survival. Historical records show the 1993 plague caused an estimated $96 million in damage across South Australia and Victoria, while the 2020-21 outbreak in New South Wales and surrounding states resulted in losses potentially reaching hundreds of millions, including impacts on machinery, infrastructure, and stored grain.

Current conditions mirror those past events but with distinct regional intensity. Western Australian growers describe roads littered with dead and dying mice, homes overrun despite sealing efforts, and cars rendered unusable after rodents chew through wiring and insulation. One resident in the town of Morawa noted the infestation had reached levels never previously experienced, with mice appearing in every corner of daily life.

Direct Impacts on Crops and Farm Operations

The timing of the surge coincides critically with the autumn sowing window. Mice vacuum up seeds almost as soon as they are placed in the ground, while any surviving plants face chewing damage at the base. Growers in the Mid West and Wheatbelt report having to re-seed entire paddocks multiple times, incurring not only seed costs but also fuel, labour, and opportunity losses from delayed planting.

Canola, wheat, barley, and lupin crops are all vulnerable. In canola paddocks, some farmers estimate losses equivalent to thousands of dollars per hectare. Beyond direct consumption, mice contaminate grain stores with droppings and urine, rendering portions unfit for market or requiring costly cleaning processes. Livestock operations face secondary risks when rodents access feed supplies or damage infrastructure such as silos and irrigation systems.

The financial toll extends beyond immediate crop losses. Professional baiting programs, often requiring multiple applications, run into tens of thousands of dollars per property. One 14,000-hectare operation in Mingenew, Western Australia, has already committed substantial resources, with the grower noting this event surpasses the severity of the 2021 eastern states plague he previously encountered.

Effects on Rural Communities and Households

Beyond the paddocks, the plague disrupts daily life in small towns and on individual farms. Residents report mice entering kitchens, bedrooms, and even water tanks, raising hygiene concerns. Dead rodents litter streets and properties, creating unpleasant odours and potential disease vectors through contact with droppings. Schools and businesses have implemented extra cleaning protocols, while some families describe constant vigilance against infestations in vehicles and sheds.

Psychological strain is significant. The relentless presence of rodents contributes to stress, sleep disruption, and a sense of helplessness among farming families already managing volatile commodity prices and weather variability. Community leaders in affected shires have highlighted the need for coordinated support, noting that the outbreak compounds existing pressures from fuel and fertiliser cost increases linked to international events.

Photo by Daniil Komov on Unsplash

Scientific Monitoring and Expert Assessment

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) plays a central role in tracking these outbreaks through its national mouse monitoring network. Research officer Steve Henry has described conditions in Western Australia as approaching or matching the worst recorded levels, with burrow counts indicating 3,000 to 4,000 active sites per hectare in hard-hit zones. This equates to mouse populations several times the plague threshold.

Forecasts issued in March 2026 flagged high risk in specific Western Australian regions and moderate-to-high activity in South Australia. The public MouseAlert platform allows growers and residents to contribute real-time observations, improving predictive accuracy for future events. Scientists emphasise that while the precise triggers for plague years remain partially understood, sequences of good rainfall and mild winters consistently precede major surges.

Long-term research focuses on improving bait efficacy, understanding mouse ecology in modern farming systems, and developing integrated management strategies that reduce reliance on chemical controls alone.

Control Measures and Regulatory Response

Farmers have traditionally relied on zinc phosphide baits at standard concentrations. In response to the current crisis, the Australian Pesticides and Veterinary Medicines Authority (APVMA) issued an emergency permit in May 2026 authorising the use of double-strength ZP50 bait containing 50 grams per kilogram of active ingredient. This stronger formulation targets areas with confirmed high populations and requires accredited training for users.

Application involves broadcasting bait across paddocks at precise rates, typically timed for late afternoon to minimise non-target impacts. Multiple rounds may be necessary as new mice emerge. Growers are also encouraged to monitor via the national network and report activity to coordinate regional efforts.

Broader strategies include habitat modification, such as reducing stubble where feasible, and community-level coordination through grower groups. While no single solution eliminates plagues, timely intervention at sowing has proven effective in limiting escalation.

More information on monitoring and management is available through official CSIRO resources and state agricultural departments.

Economic and Broader Implications

Australia ranks among the world's leading wheat exporters, and sustained damage to the 2026 crop could influence global grain markets already sensitive to supply disruptions. Potential losses in the hundreds of millions of dollars are being discussed by industry bodies, echoing the scale of previous events. Export contracts, domestic feed supplies, and downstream processing industries all face ripple effects.

The outbreak also intersects with environmental and trade considerations, including ongoing discussions around sustainable farming practices and biosecurity. While mouse plagues are a natural occurrence, their frequency and intensity in recent decades have prompted calls for enhanced preparedness and research investment.

Future Outlook and Preparedness

Experts anticipate that populations may begin to decline naturally once food sources diminish or colder conditions arrive, but proactive management remains essential through the current season. Continued monitoring via CSIRO-led programs will guide decisions on whether additional interventions are required in coming months.

Longer-term resilience depends on sustained investment in predictive tools, improved bait technologies, and farmer education. The integration of citizen science through apps like MouseAlert represents a positive development, empowering communities to contribute to national understanding.

For those in affected regions, staying informed through local agricultural networks and official government channels provides the best pathway to mitigating further losses. The current situation underscores the challenges of farming in Australia's variable climate and the importance of adaptive strategies.

Photo by Tarryn Grignet on Unsplash

Stakeholder Perspectives

Farmers across the impacted zones express a mix of frustration and determination. Many describe the outbreak as one of the most severe in living memory, with costs mounting daily. Industry representatives have welcomed the emergency bait approval while urging swift distribution to properties in need.

Local government officials in Western Australia have advocated for additional support measures, highlighting health and amenity impacts on entire communities. Scientists continue to stress the value of data-driven approaches, noting that early action at the first signs of increase can prevent full-scale plagues.

These perspectives collectively illustrate the multi-layered nature of the challenge, spanning individual farm viability, regional economies, and scientific understanding.