Stock Sense with Paul McKee Ravensdown Technical Manager

Insect Growth Regulators have been revolutionary chemicals in the management of flystrike in sheep.

These chemicals (cyromazine, dicyclanil, triflumuron and diflubenzuron) work by interfering with the maggot’s ability to complete the moulting process during development leading to eventual death.

The ability for farmer’s to apply a user friendly preventative treatment that could protect stock from strike for up to 16 weeks meant huge savings from the direct and indirect costs associated with flystrike.

The emergence and spread of flies resistant to two of the IGRs (triflumuron and diflubenzuron) has seen reductions in the length of protection down to as little as one to two weeks in some areas. While other products remain effective in treating flystrike, only the IGRs provide long term protection from fly attack.  

The prospect of losing the IGRs ability to provide stock with long term fly protection is a worry for the industry. Protecting the remaining IGRs that are effective from the development of resistance will be critical. This is best achieved through a combination of non-chemical and chemical means.

Reducing the need for treatment through good stock management is going to be important, including; effective worm control, dagging and monitoring of fly numbers. When chemical treatments are required, farmers must follow manufacturer’s guidelines for rates and methods of applications. Halving the dose, using gorse guns, running too high a pressure in spray units, too long a wool length and failing to get saturation are all likely to contribute to the reduced efficacy of treatments and increase the pressure for the development of resistance.

More recently the development of combination products will hopefully further reduce maggots surviving treatment and develop chemical resistance. No one wants to go through all the effort of having to retreat stock because of resistance.