Dairy farmers are being urged to tackle fly breeding sites now, as warm summer conditions accelerate larvae development in straw-bedded calf pens and hutches.

Dave Reece, Lodi UK pest control technical adviser, says recent high temperatures, particularly overnight, are creating ideal conditions for fly larvae to develop, with some populations able to hatch in as little as eight to nine days.

He warns that while flies are often first noticed in the parlour, the problem usually starts much earlier in youngstock housing.

“Flies are often noticed in the parlour because that is where they cause the most disruption, but it is rarely where the problem starts,” says Mr Reece.

“On dairy farms, straw bedding in calf pens and hutches is one of the most common breeding sites.

“Over the past couple of weeks, we’ve been peeling back straw and finding white maggots and larvae underneath.

“In warm conditions, those larvae can hatch in as little as eight to nine days, so fly numbers can build rapidly if control measures aren’t in place.”

Once adult flies emerge, they move towards collecting yards and milking parlours, attracted by warmth, animals and carbon dioxide.

Mr Reece says fly control needs to start in housing, rather than relying solely on reactive treatment in the parlour.  

“Calves irritated by flies are less likely to lie down and rest, which can affect growth and welfare,” he says.

“Flies can also move disease from animal to animal, so even where biosecurity is good, they remain a risk.”

Mr Reece recommends an integrated approach, combining hygiene, larvicide treatment and adult fly control.

“Keep calf pens as clean and dry as possible, clean and disinfect between animals, and clear up after spilt milk,” he says.

“It’s important to pay attention to the edge of pens and hutches too, as flies often hatch around these areas.”

Where fly pressure is very high, pens may need to be cleaned out almost weekly to help break the breeding cycle.

Mr Reece also advises using two larvicide treatments during a calf-rearing cycle, with the first about 10 days after calves enter the pen and the second around a month later, to help break the fly life cycle before maggots develop into adult flies.    

Where adult flies are already present, he says Ultra Dairy Fly Spray can be applied to calf hutch roofs, in line with label instructions, to provide knockdown and residual control.

In parlours, it should be applied to walls, roofs and resting areas before cows enter, and high enough to avoid being affected by washdown.

For further advice on managing flies this season, contact Lodi UK or visit insect and fly control solutions.