Available chemicals for flystrike prevention fall into different chemical groups. Insect Growth Regulators (IGRs), Macrocyclic Lactones (MLs), Synthetic Pyrethroids (SPs), Spinosyns, and most recently Neonicotinoids such as Avenge®. Organophosphates (OPs) have been widely used for flystrike treatment and prevention in the past however OP resistant blowfly have become common. Newer chemicals are highly effective and have fewer human and animal health safety risks. There are also different options in delivery methods including backliner, spray on or jetting fluid. Treatments can be applied at different times depending on the presence of flystrike potential. Some chemicals can be applied in short wool (even off shears) or in long wool.
Avenge® (imidacloprid) is approved for flystrike control and provides up to 10 weeks protection against body and breech strike when applied in short wool (up to seven days off shears) or up to 14 weeks protection when applied in long wool (6 weeks to 8 months).
When to treat for flystrike prevention
It is important to be vigilant when climatic conditions are suitable for flystrike. Regular monitoring of the flock for struck sheep and the use of fly traps to monitor fly activity and numbers are all valuable. By the time obviously struck sheep are detected fly numbers have already increased. Ideally, with a knowledge of climate and other factors predisposing to flystrike, preventive treatments should be applied in anticipation of this occurring.
Apart from organophosphate compounds (OPs), there has not been resistance detected in sheep blowflies to the other chemical groups. Nonetheless, to avoid resistance developing it is important to use all chemicals according to recommendation, do not under dose and avoid over reliance on chemicals from a single chemical class. Use of chemicals with a shorter period of protection at times of the year when fly pressure is declining may give the other chemical groups a rest and slow down selection for resistance.