Flystrike is a common problem on many farms over the summer months and is an issue no one really likes dealing with.

So what is new in flystrike control? We all know that drench resistance is an issue but have you ever thought about resistance in relation to fly products?

In a nutshell, there are 3 different families of chemicals available to treat/prevent fly and lice issues.

  • Organophosphates (Ops)
  • Act to quickly kill maggots and lice but have short term fly control and are not very safe.
  • Levamisole should not be used at the same time (e.g. Xterminate, Flypel)
  • Insect Growth Regulators (IGRs)
  • Stop the development of flies, maggots and lice
  • IGRs are commonly used as preventative products
  • 3 different chemicals -triflumuron, cyromazine, diflubenzuron (e.g. Cryazin, Fleecemaster, Exit)
  • Synthetic Pyrethroids (SPs)
  • Kill lice and maggots, and deter flies from depositing eggs
  • Mainly used as pour-on lice preventatives off the shears (e.g. Cypercare and Flypel)

There are 3 main species of blowfly that can initiate flystrike in sheep – common green, Australian green and the brown blowfly.

  • Australian Green Blowfly
  • Common Green
  • Blowfly Brown Blowfly

For the last two years, Tararua Vets has been involved in a fly research trial in conjunction with Novartis. This has involved collecting maggots from flystruck sheep and sending them to the lab where they have been grown and tested against two commonly used fly chemicals at differing strengths. The outcome of the trial confirmed that there is resistance in NZ to at least 2 chemicals used to protect against fly. Initially, most of this resistance was centred around the Raglan area, however last year some of these resistant flies were found in Wanganui. All of the samples collected in this area over the last 2 years have been susceptible to low chemical does, however, Wanganui is not far away.

Given this, it is worth giving consideration to changing the products you use ion controlling/preventing flystrike on your farm. The good news is that there are now two combination products available to help combat both fly and chemical resistance. Call in and have a chat about the best options for your farm.


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