The CSIRO has warned that mouse populations have exploded across parts of regional Australia, but the cause of the outbreak remains a partial mystery. Farmers in Western Australia and South Australia are reporting sightings that evoke memories of the devastating 2020-21 mouse plague, which caused an estimated $1 billion in damages across eastern Australia. As growers prepare for the seeding season, concerns are mounting over the potential impact on crops, stored grain, and farm infrastructure.
According to CSIRO research officer Steve Henry, mouse numbers in Western Australia have reached levels not seen since the 2021 outbreak, with reports of up to 4,000 mouse burrows per hectare in areas around Geraldton and the state’s wheatbelt. Henry stated that more than 800 mice per hectare is now considered a plague under any circumstances, and the current situation in Western Australia meets that threshold. “In Western Australia we’re now using the P word,” he said, confirming that the term “plague” is being applied to the current surge.
In South Australia, the Adelaide Plains and Yorke Peninsula—including Kangaroo Island—are experiencing increasing mouse densities, with some areas showing potential for outbreak depending on environmental conditions. Henry noted that mouse numbers on the Adelaide Plains are “extremely high” and “very concerning for farmers,” with trapping efforts revealing between 100 and 200 mice per hectare in some sites, and up to 400 to 600 per hectare where trap saturation occurs. Farmers like Matt Davey, who works on the northern finish of the Yorke Peninsula, said current levels are the worst he has seen in four or five years, attributing the increase to recent moisture following several dry seasons.
The timing of the surge is particularly concerning as it coincides with the traditional start to the seeding season. Mice pose a significant threat during this period as they will follow furrows created by seeding equipment and consume newly planted seeds before they can germinate. This behavior not only reduces crop yields but also increases the need for reseeding, adding to input costs at a time when farmers are already managing pressures from diesel prices and fertiliser availability.
Beyond immediate crop losses, mouse plagues bring broader risks to farm operations and rural communities. The 2020-21 plague demonstrated how rodent infestations can contaminate feed and water supplies with urine and carcasses, posing health risks to livestock. Human exposure to pesticides used in baiting efforts increased during that event, and both people and domestic animals faced elevated risks of disease transmission. Psychological strain on farming communities was also widely reported, with prolonged periods of high rodent activity contributing to stress and fatigue.
In response, the CSIRO is urging farmers to monitor mouse activity closely and consider applying baits at the time of seeding in areas of high activity. The agency also recommends reducing the availability of alternative food sources, such as spilled grain or ground cover, to limit breeding opportunities. While baiting remains a primary tool for managing outbreaks, officials stress the importance of following label instructions and safety guidelines to minimize unintended impacts on non-target species and the environment.
As of late April 2026, the CSIRO’s mouse forecast indicates that populations are expected to remain low through most of Recent South Wales and Victoria, offering some relief to growers in those regions. However, the focus remains on Western and South Australia, where conditions are being monitored weekly. The agency continues to collect data through trapping programs and farmer reports to refine its predictions and guide regional responses.
The situation underscores the ongoing challenge of managing native rodent populations in agricultural landscapes, particularly as climate variability influences breeding cycles and survival rates. While the exact drivers of the current surge are not yet fully understood, the combination of recent rainfall, available food sources, and favorable breeding conditions appears to be supporting rapid population growth. Experts note that female mice can start breeding as early as six weeks of age and produce litters of up to 10 young every three weeks under ideal conditions, enabling numbers to escalate quickly.
For farmers navigating this renewed threat, access to timely, localized information is critical. The CSIRO regularly updates its mouse forecast and provides guidance through its website and direct engagement with agricultural bureaus. Growers are encouraged to report sightings and participate in monitoring efforts to help build a clearer picture of regional risks.
As the seeding season progresses, the coming weeks will be pivotal in determining whether the current activity remains localized or expands into a broader outbreak. With no single cause identified yet, the response relies on vigilance, early intervention, and community-wide coordination to protect both agricultural output and rural livelihoods.
Stay informed about the latest developments in Australia’s mouse situation by consulting official updates from the CSIRO and your local agricultural authority. Share your observations and experiences to help others in the farming community stay prepared.