On livestock farms, flies are not merely a nuisance. They are disease vectors affecting animal health, productivity and the farm standards that must pass audit.

Insecticide fogging is therefore a strictly scheduled routine, and when the schedule is followed but results do not improve, most people conclude either that the chemical is poor or that the pests have developed resistance.

But there is another cause, far more common than people expect and very easy to check: chemical sediment accumulating in the tank and delivery system, which makes what actually leaves the nozzle far weaker than intended.