Free testing of farm rodenticide resistance status

25 March 2021

Farmers, UK-wide, are being called upon to help create a more accurate national picture of resistance to rodenticides in rats and mice. In return, they will get a free indication of their farm’s status from the Campaign for Responsible Rodenticide Use UK (CRRU).

This appeal comes about due to the “surprising and troubling” spread of resistance to rodenticides found by CRRU’s latest surveillance. It found, not only, that three-quarters of rats analysed carried a resistance gene, but one-in-five had two different genes, known as ‘hybrid resistance’.

This hybrid resistance poses potentially unknown difficulties for rodent control. CRRU chairman, Dr Alan Buckle said: “A critical practicality is that, where resistant rodents are present, farmers could be using products that are ineffective. And where resistance genes are still absent, others may be using resistance-breaking products unnecessarily.”

What to do

This appeal is asking farmers to collect 2-3cm tail ends from freshly deceased rats or mice and send them by post in free packaging kits. These are available, with detailed instructions, from CRRU. Visit the Stop the spread of resistance page on the Think Wildlife website for more information.

Resistance testing is a formal component of the CRRU-operated UK Rodenticide Stewardship Regime. As a measure of the regime’s success, rodenticide residues in barn owls are also monitored. The most recent results were 87% residue-positive.

Impact on wildlife

This year will see a formal in-depth review by the regime’s Government Oversight Group of its implementation and impact on wildlife. To be judged effective, lasting reductions in rodenticide residues carried by non-target wildlife are expected.

Without such evidence, Dr Buckle suggests the possibility that further restrictions could be applied to how rodenticides can be used, and by whom. “Clearly, this places responsibility squarely in users’ own hands,” he says.

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