Fly Control in the Spring and Early Summer

Flies in both cattle and sheep can as a minimum, cause significant production losses but if left unchecked can lead to death in the most severe cases. The reality is that a lot of the issues can be avoided if there is a suitable management protocol in place.


Blowflies are the most widespread ectoparasite affecting sheep in the UK, with surveys showing that every year 80% of flocks will have one or more cases of strike. If not properly controlled, this will result in serious welfare problems and reduced profitability in up to 500,000 sheep.

As I write this in mid-April we have already seen the first case of fly strike in Pembrokeshire. We normally expect to see blowfly strike between May and September but with changing weather patterns, lowland flocks are at risk from March through to December. With increasing flock sizes and the need to rationalise labour use to improve profitability, flocks must have a plan that will provide protection during the risk period and fit with the need to control other parasites.


Like most suppliers CCF stock a number of products that treat and protect against fly strike. Some have activity against other ectoparasites as well. They have different modes of action and consequently differing lengths of protection so advice is essential to ensure you use the best product for your flock. The products are all different so always read the manufacturer’s instructions on dose rate, storage and withdrawal periods. Check application equipment is working properly and is calibrated. Replenish dips according to instructions and follow all safety guidelines.


Good management and planning can help to reduce the risk of strike occurring. Most strikes (over 70%) occur around the breech or tail where there is faecal and/or urine soiling as these are very attractive to the flies. Wet weather can lead to strike on the backs of unshorn ewes and lambs and footrot can lead to strike in the feet.

Tips that can reduce strike issues:

  • Dag to reduce soiling and/or remove dirty wool around the breech
  • Reduce the incidence of soiling by avoiding nutritional upsets causing scouring and have a sound worm control strategy
  • Tail dock the sheep
  • Avoid breeding from sheep that are habitually struck and/or tend to soil themselves due to their conformation
  • Try to keep sheep away from sheltered fields in the high risk periods
  • Reduce the incidence of footrot



Cattle also have problems with flies although the issue is more to do with production losses as opposed to chronic disease although flies do spread summer mastitis and eye disease.

All types of flies breed in dung and organic material and the development time from egg to adult can be as little as eight days in summer, rapidly producing large populations. Under typical UK climatic conditions, up to 15 generations of flies can be produced in just one year. This means that the peak fly populations are usually in July and August. However, with unpredictable weather patterns, fly problems can start in April and last into October.

By controlling the environment in which flies breed, fly populations on farm may be reduced. Reducing fly breeding sites like muckheaps as well as keeping the yards clean can help. Think about keeping cattle away from sheltered fields in the summer period especially if there is water present.

Chemical methods can also play a valuable role in controlling the fly population by breaking the fly life cycle. As adult flies are only 20% of the total fly population, with immature eggs accounting for 80%, it is advisable to use a larvacide and adulticide concurrently. Larvacides will kill the larvae (maggots) and stop larvae from continuing their development into flies. Adulticides are ‘knock down’ products that kill flies on application which will continue to kill flies after application.

For on animal control of flies, the choices are either insecticide-impregnated ear tags or Pour-on products which are normally synthetic pyrethroid insecticides.

Animal health suppliers can help with product selection but a top tip is to tackle the problem early. Not wait until the flies become a problem.