Computer forecast for summer fly strikes soon

3 May 2002

Computer forecast for summer fly strikes soon

By Richard Allison

SHEEP and dairy herds are facing the early threat of fly strike this season with first strikes hitting many lowland flocks in the next two weeks, according to a new web-site* launched this week.

The computer program is designed to forecast patterns of fly and disease incidence, says its developer, University of Bristol zoologist Richard Wall. "It works by combining daily temperature and rainfall data to predict when fly-strike will first occur."

For many years, it has been an effective tool accurately predicting the start of the blowfly season to within a week. This allows producers to take action at the correct time, ensuring effective blowfly control in their flock, says Prof Wall.

Early indications suggest that recent warm, dry weather has brought forward the start of the blowfly season to early May. "Many lowland flocks will see the first strikes in the next few weeks, depending on local conditions."

Based on this prediction, Cheshire-based independent sheep vet Chris Lewis advises preventative treatment of ewes and lambs before flies emerge. "A few blowflies have already been seen flying around flocks."

Timing is crucial; its more difficult to control once fly populations have built up. However, producers must also take their location into account, first strikes gradually become later as you move further north and onto higher land, reflecting lower temperatures, he explains.

Many experts believe blowfly is not a serious problem in upland areas. But Mr Lewis believes hill flocks can still suffer from severe flystrike later in the season, about mid-summer.

The best strategy is dipping sheep in spring and autumn with organophosphate dips, says Mr Lewis. "I always use OP dips to prevent blowfly strike in my flock as it also controls scab mites and lice, which persist on animals during warmer months.

In addition to using insecticides, preventing scouring in lambs by avoiding high worm pastures and ensuring ewes are dagged will help avoid blowfly strike. "Fleeces soiled with urine and faeces attract flies."

However, its not just blowflies that are early, believes Prof Wall. "There is a good chance that other biting insects will strike livestock earlier due to the warm, dry April weather."

To minimise fly strike and associated summer mastitis in dairy cattle, Somerset-based dairy vet Peter Edmonson recommends placing dry cows and heifers in fields away from water and trees. "Ideally in fields on top of a hill."

Also, check animals at least once daily for signs of fly attack and summer mastitis. "Any affected animals should be quickly removed to minimise spread of mastitis by flies."

Fly treatments will help, but they only reduce fly numbers and cannot eliminate them all. He is concerned that relying on ear-tags maybe unwise, as cows need two tags for effective control and they are at the opposite end of the cow to the udder. Pour-on treatments, however, offer good control.

Many dairy producers are reassessing their strategy by considering natural alternatives to OP fly treatments, says Neutra Genes Jonathan Guy. "This was prompted by the recent banning of dichlorovos containing OP fly products due to fears over skin and liver cancer."

In one recent study at Derby-based Broomfield College, a magic eye system to deliver a natural non-kill spray onto dairy cows was investigated. "It is a device similar to the infra-red sensor on security lights. When a cows passes the sensor, it sprays a mist onto her back to repel flies."

"The system proved effective, even providing fly control when outside grazing after milking," says Mr Guy.

However, Mr Lewis warns producers to be careful when considering alternative treatments. "Ensure they are either POM or PML products and have been properly assessed for their effectiveness."

*The website is sponsored by Coopers Ectoforce and also provides information on treatment strategies (www.strike &#42


* Earlier blowfly season.

* Prevention more effective.

* Summer mastitis risk.

&#8226 Earlier blowfly season.

&#8226 Prevention effective.

&#8226 Summer mastitis risk.

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