Pesky Flies

flock of sheep in paddock

What a year we had last year! We are all hoping that there will not be a repeat of the high level of fly strike in our stock.

It is such a huge stress to the stock and the farmers alike. So what is going to happen this year? Well I don’t know for sure, but we do know some things…

• When soil temperatures get to 15 degrees the larvae will start to hatch.
• Flooding and trampling over winter will reduce fly populations from one year to the next.
• Pupae will have been dropped into the soil in areas where struck sheep were last year.
• Flies are more prevalent in warm wet environments.
• Less fly strike will occur in windy areas.
• Shearing gives about 4 weeks protection against fly strike because the sun gets through to the skin and kills the eggs.
• Fly traps are best for letting you know when flies are around – also cooking a Sunday roast.
• Label claims for length of activity are a guide only – act on what you see.

Local conditions

In the first week of November, Gore soil temperatures were around 12 degrees, and at Heddon Bush they were around 13 degrees. So, assuming that things continue to warm up, we may not be too far away from he larvae starting to hatch. Once you start seeing flies in your house (not cluster flies) your stock will become at risk.

Treatment of strike

There are a couple of products that treat a struck animal. One is an organophosphate (Maggo) – it works very quickly to kill maggots. However, be very careful, as it works on the nerve system of the flies – and it does similar things to people as well. The jumping around the ewe/lamb does when getting treated is the nerve endings being stimulated – not very nice. The other product is Cyrex. This product stops moulting of the larvae which means there is not immediate kill. However, any eggs that hatch can only become first stage larvae – which do not penetrate the skin. Death of the maggots is not so instant, but it is much safer for the animals and people. A new batch needs to be made each day. Both are available in our shops.


Prevention is likely to be needed this year. Shearing will give you 4 weeks ‘grace’ period as the sun will penetrate the skin for this time and kill any eggs that are laid. After that, it is likely you will need to dip with something. The products we have available are;

Product Use Meat WHT

  • Cyrex* Treatment and prevention 7 days
  • Cyrazin* Prevention 21 days
  • Clickzin Spray On* Prevention 7 days
  • Magnum Prevention NIL
  • Zap Encore Prevention 49 days
(*No resistance in flies)
Meat with hold will be important for lambs and cull ewes. It is great there are products that can be used in these situations. Remember that any wounds must be healed before animals are sent to the works (even if they are not under a meat WHT).

What can go wrong with managing fly?

Farmers often tell us they have not had the expected response to treatment. This can be for a variety of reasons;
• Poor application – the whole animal is not wet to the skin.
• Rain has fallen and washed some of the product away.
• Not enough wash has been used, or sheep running through too fast.
• Volume of dip not increased for longer wool.

We are all hopeful that the fly problem of last year is not the start of an ongoing problem for us here in the south. Only time will tell. If you would like to discuss your situation and create a plan, please ring us and we can organise a time to create a whole farm approach to managing fly for you.

- Donna Hamilton


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