Farmers fear potential mouse plague as CSIRO warns of high numbers

Lead

Australian grain growers are on high alert as mouse numbers surge in Western Australia and South Australia, with the CSIRO warning of potential plague conditions. In Western Australia, farmers report infestations of up to 8,000 mice per hectare in the northern grain belt, while South Australian growers are seeing increasing activity ahead of the traditional seeding start. The situation has renewed calls for access to a stronger zinc phosphide bait, which farmers say is being blocked by regulatory hurdles.

Coverage Comparison

Reports from ABC Australia and The Guardian highlight the severity of the mouse problem, with each outlet focusing on different regional aspects. ABC's coverage of Western Australia emphasizes the frustration of farmers who say current poison dosages are ineffective, while its South Australia report details the CSIRO's projections of high mouse numbers in parts of that state. The Guardian's global edition frames the issue within the context of historical mouse plagues, noting that they occur every four to five years and can cause devastating economic damage.

Key Claims

• Mouse numbers in Western Australia have reached plague proportions. According to CSIRO researcher Steve Henry, more than 800 mice per hectare constitutes a plague, and reports from Western Australia indicate 3,000 to 4,000 burrows per hectare in some areas. ABC Australia reported an estimated 8,000 mice per hectare in the northern grain belt.

• Current zinc phosphide dosages are not working. Grain growers in Western Australia say the standard 25 grams per kilogram concentration is insufficient, and a double dose of 50 grams per kilogram is needed. John Warr, a farmer near Yuna, told ABC that mice need to eat at least two baits with the standard dose to die, whereas one bait with the higher rate would be lethal.

• The APVMA is refusing to allow the manufacture of double-dose baits. The Australian Pesticides and Veterinary Medicines Authority has rejected applications for emergency permits from manufacturers and Grain Producers Australia, citing that the CSIRO research supporting higher rates is "not of sufficient regulatory quality." Warr described the decision as "dumbfounding," given the recurrence of mouse plagues over the past decade.

• CSIRO research supports higher rates of zinc phosphide. The application for the double-dose bait cited CSIRO studies on the improved efficacy of higher concentrations, though the APVMA has not accepted this data as sufficient.

• Mouse numbers are increasing in South Australia. Farmers on the Yorke Peninsula and Adelaide Plains have reported rising activity, with CSIRO projecting "high" mouse numbers in parts of the state. Research officer Steve Henry said some sites are seeing 100 to 200 mice per hectare, with trap saturation in others reaching 400 to 600 per hectare.

• Mouse plagues occur in Australia every four to five years. A study cited by The Guardian notes that significant outbreaks often follow several years of below-average rainfall, which creates abundant food sources for mice. The 2020-21 plague in eastern Australia caused an estimated $1 billion in damage, according to The Guardian.

Perspectives

Farmers' perspective: Growers in Western Australia and South Australia are concerned about the impact on crops and property. Matt Davey, a farmer on the Yorke Peninsula, described the mouse levels as the worst he had seen in four or five years, with mice eating seeds as they are planted, leading to "UFO rings" of bare ground around their holes. John Warr highlighted the social and welfare implications, noting the pervasive smell of dead mice in homes and sheds.

Regulatory perspective: The APVMA has not commented publicly on the specific applications, but its rejection of the emergency permits suggests a cautious approach to approving new pesticide formulations. The authority's stance is that the data provided does not meet regulatory standards, a position that farmers and grower groups dispute.

Scientific perspective: CSIRO researchers like Steve Henry emphasize the need for monitoring and proactive baiting, especially at seeding time. The latest CSIRO forecast recommends farmers monitor activity, apply baits in high-activity areas, and reduce alternative food sources. Henry noted that the current situation could escalate rapidly, as female mice can breed from six weeks old, producing up to 10 babies every 19-21 days.

Conclusion

As farmers in Western Australia and South Australia prepare for seeding, the threat of a mouse plague looms large. The combination of high mouse numbers, regulatory delays, and the potential for rapid breeding has created a tense atmosphere. While the CSIRO provides guidance and forecasts, the resolution of the bait controversy remains a critical factor in mitigating potential damage. The situation underscores the ongoing challenge of managing agricultural pests in a changing climate, where historical patterns may no longer reliably predict outbreaks.