Livestock farmers should be aware that mild wet weather could maintainviable breeding conditions for two important fly species well into November.

BlowflyAccording to entomologist Peter Bates, formerly of the VLA and now independent proprietor of the Veterinary Medical Entomology Consultancy, this applies to two types of fly in particular with a marked impact on animal health, welfare and performance: biting house flies and blowfly.

Dr Bates said: “In contrast with single generation fly species whose numbers have peaked and declined by now, these two will continue breeding for as long as conditions allow.

“To curtail their activity now, we need either an Indian summer of prolonged dry weather, or a decent cold snap with temperatures consistently below 10°C.”

With the more likely scenario for many parts of the UK being “another couple of months of mild wet weather”, Dr Bates claims fly numbers could persist through October and into November.

According to Pfizer VPS vet Dave Gilbert, this means fly control around livestock remains both justified and necessary. In cattle, he claims, fly nuisance has been shown to reduce milk yields by up to 0.5 litres/cow/day or growth rates by 0.3kg/head/day. Consequently, where conditions continue to favour the fly population, there is a good case for an autumn treatment with a long-acting pour-on pyrethroid, which can provide protection for up to eight weeks.

CarcaseLooking ahead, Dr Bates claims there are simple steps that farmers can take to restrict the breeding sites available to flies, such as the prompt collection and disposal of carcases, including wild animals.

He said: “In addition to obvious fly-friendly places like dung heaps and slurry stores, other sites offering a combination of moisture and organic matter can provide both a favourable breeding ground and a hospitable over-wintering site for larvae and adults.

“Often overlooked by farmers is that wet hay or straw can be a breeding place for flies. By eliminating such avoidable breeding grounds, a marked impact can be made on next year’s fly populations and their detrimental effects on animal health, performance and welfare, not to mention the workforce’s comfort and productivity.”

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