VETERINARIAN Rosemary Longuett-Higgins at King Country Vets.
Let me preface this by saying: this is a dry piece of writing. However, I hope it is informative and helps guide your fly protection plan this season.
Products available in New Zealand:
Organophosphates – still around, a very old chemical class. High level of fly resistance. Smell terrible, offends rams at mating so much that it may impact reproductive outcomes. High environmental, animal and human toxicity.
Synthetic pyrethroids – mainly for lice. High level of resistance, so work poorly and don’t last long.
Insect Growth Regulators (IGRs) – the majority of products available fall into this category. IGRs work by preventing maggots from developing, and thus from causing a strike. There are two groups of IGRs, one with lots of resistance (BPUs) and one with good efficacy.
The BPUs are diflubenzuron and triflumuron. Both have a high level of fly resistance in the Waikato (since 2008), so you are unlikely to get adequate protection from products containing these actives. They are highly toxic to soil and aquatic invertebrates and are very persistent in the environment. Some combinations of diflubenzuron/triflumuron are available from other stockists, and we advise not to use these for the reasons above. Overall, there are many more appropriate and efficacious fly prevention options available than BPUs.
The triazine and pyrimidine derivatives are cyromazine and dicyclanil. These are preventative treatments on their own, but combination products are available for treating sheep already affected by flystrike. Cyromazine and dicyclanil have very good efficacy in New Zealand when applied correctly, and there are various formulations for different lengths of protection and meat withholding periods. They have a low environmental toxicity.
Ivermectin – used in combination with cyromazine for extended protection and maggot killing (treating struck sheep).
Imidacloprid and Spinosad – fairly new products, come alone or in combination with IGRs. No documented resistance.
The big question – what do we recommend?
Preventative treatment. Easier said than done, considering the timing of shearing, wool and meat withholds. However, given the welfare and production implications of flystrike, it’s not acceptable to have routinely flystruck sheep, and the welfare of your flock trumps voluntary wool withholds when necessary.
Use a product that works. For most of the Waikato-King Country, that excludes organophosphate, diflubenzuron and triflumuron products. Talk to your vet about effective products in your area and the options available for different stock classes. Beef & Lamb NZ have excellent online resources for understanding flystrike, its treatment and prevention.
Choose something you can apply correctly. Incorrect application of fly products results in poor fly control, reduced duration of protection and ultimately drug resistance developing in the fly population. With only a few effective chemicals left, much like with drench resistance, we need ensure we protect their efficacy.
Using too little of a liquid product, for example 1.5L on 6-month length of wool in a MA ewe, leads to lower concentrations of active ingredient within the staple/lanolin and subsequent low dosing of larvae and resistance development.
Implement preventative management practices such as selecting low-risk paddocks, monitoring and reducing fly numbers with fly traps.
Treat for lice and fly separately or you aren’t doing a good job of either. Select separate products and dipping opportunities for the best control of fly and lice. Lice treatment must be done off-shears. Whereas fly treatment requires a minimum of 3-4 weeks wool growth after shearing to build up lanolin for the chemical to bind to (and give you the long action you need).
