Stock farmers warned to prepare for early fly threat

Sheep and cattle farmers should prepare for an earlier and more prolonged fly season following a mild and wet winter.

Biologist Dave Goulson, from the University of Sussex, has warned an earlier season will increase and speed up breeding.

Met Office figures show November, December and January were all wetter than normal, and February temperatures averaged 5.1C across the UK – 1.4C above the long-term national average.

Prof Goulson said he expected flies to get off to an early start. “When the weather is mild, flies will become active earlier in the year and will breed more within the same timeframe, resulting in an extended active fly season.”

Vet advisers are warning that fly hatches commence once temperatures pass 10C.

Parasite tracker

The Zoetis Parasite Watch scheme this year includes 26 farms that are using fly traps to monitor on-farm fly populations.

Read more by visiting the Parasite Watch page.

Act early

Stephanie Small, MSD Animal Health dairy veterinary adviser, said early treatment was important to prevent adults laying further generations of eggs that could result in population explosions.

“Flies can cause distress, known as fly ‘worry’, severely reducing milk yield because it causes restlessness and reduces the time cows are eating,” she said.

“It’s estimated this reduction can be as much as 14,700 litres of milk per 140-cow herd over 10 weeks.

“These pests also transmit dangerous diseases, such as summer mastitis, later in the year, so control is vital.” 

Zoetis vet Ally Anderson said it is far easier to control flies before they become a problem.

“For all treatments, it’s important to speak to your vet or SQP to find out more,” she advised.

She said studies have shown fly worry can lose between 0.3-0.5 litres of milk a day in dairy cows and more than 5.5kg of a sheep’s liveweight can be lost over a four- to six-week period.

Treatment guide

Farmers have a range of options to consider, with the best option depending on the type of fly. It’s important to manage dung effectively, advises Control of Worms Sustainably (COWS).

Flies vary around the farm, with the following locations home to the following flies:

  • Pasture soil and pasture dung Hydrotaea irritans and Musca autumnalis
  • In sheds Stomoxys calcitrans
  • Dung heaps Biting midges

Insecticide-impregnated ear tags and tail bands containing pyrethroids and pyrethroid pour-on, spot-on and spray preparations are all good options.

Farmers must remember to check the duration of the actives and any withdrawal periods, although several fly treatments for dairy cows don’t have a milk withdrawal period.

COWS advises it is important to commence treatment early in the season and repeat according to the manufacturer’s instructions.

Fly numbers indoors can be controlled with screens and electrocution traps. Aerosol sprays and residual insecticides on walls can also reduce fly numbers inside.

Read our guide on fly control in cattle

A range of options are available, but plunge-dipping in organophosphate (diazinon) will help prevent flies as well as all other key ectoparasites in sheep, according to the National Animal Disease Information Service (Nadis).

Farmers should check the length of the action of the product and the withdrawal period before making a decision.

Pour-on, spray-on and spot-on options are available, and can be a useful way of offering protection to your flock, Nadis advises.

  • Products with cypermethrin or alpha cypermethrin will treat and protect against blow fly strike.
  • Products containing dicyclanil or deltamethrin will offer protection against blowfly strike, but won’t treat existing infections.