Warm weather brings flystrike

No one size fits all approach

Tablelands Telegraph – December 2020

While the weather this season has been a lovely change from the brown dust and smoke of last year, it brings with it a range of animal health problems. Warm, wet weather is ideal for flystrike, and the vet team has had a number of enquiries about flystrike products over the last few weeks.

There is no “one size fits all” approach to managing flystrike, as the strategy used will depend on the enterprise’s terrain, climate, sheep breed and type, shearing time, management procedures such as mulesing, crutching, and so on. A multifactorial approach of reducing sheep risk factors and strategic chemical use is important.

Reducing the sheep’s susceptibility to flystrike can involve timing shearing to ensure sheep are in short wool during high risk periods, or strategic crutching if they have long wool. Breeding for reduced wrinkle and fleece type is important in merinos. Controlling diarrhoea through good internal parasite management reduces dag and therefore the attractiveness of the sheep to flies.

The other half of the equation is chemical control. While there are many registered products on the market, it really boils down to a handful of active ingredients.

  • Spinosad (eg extinosad) this provides a short period of protection, but has short meat withhold periods and wool handling intervals. It can by applied by jetting, dipping, or as a dressing.
  • Ivermectin (eg Iverlab, Jetgard, Zinjet) provides a medium period of protection of around 12 weeks, with meat withhold of 7 days and a variable wool handling interval between products. It is the only product registered that can be used on sheep that will be used for milk production, although it has a milk withhold of 28 days. Applied by jetting or as a dressing.
  • Imidacloprid (Avenge) provides a medium period of protection of 10-14 weeks with a 21-day meat withhold and a two month wool handling interval. Can be used on long or short wool, as a spray on.
  • Cyromazine (eg Vetrazin, Clout, Flyshield and many others) provides a medium period of protection of around 14 weeks, but has a longer wool handling interval of around two months. Application methods are spray-on, jetting and dipping.
  • Dicyclanil (eg Di-fly, Luci-guard, Defend, Clik and many others) provides a long period of protection of over 18 weeks, but also has the longest withholds. Applied as a spray on.
  • Diazinon (eg Coopers Flystrike powder, KFM blowfly dressing) is used as a dressing. There are populations of flies resistant to this chemical.

The FlyBoss® website has some great tools for modelling the effects of management procedures and chemical application on fly populations and therefore flystrike risk at a specific location. By changing factors in the simulation such as shearing time, crutching time(s) and the chemical(s) applied, users can devise strategies to minimise the risk of flystrike without risking their sheep.

To discuss flystrike management in your area, please contact your local district veterinarian.

Information is correct at time of publishing. Always check the product label before use for current product information.

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