You control fly eggs best with predatory mites. Rooijakkers: “The predatory mites themselves are not spreaders of disease, but they eat the fly eggs so that the eggs will no longer transform into larvae.”
The fly larva (or maggot) itself has three stages. It isn’t easy to control all stages of the fly larva with biocides. Rooijkakkers: “We recommend a combination of robber flies, which eat the larvae, and Predal. Predal creates a bacterium in the larva, causing it to die. The larva of the robber fly eats the fly larva, while the robber fly itself does not cause any nuisance.”
In the fly’s third stage of its life cycle, the larva turns into a brown, cylindrical pupa. “You need the parasitic wasp to control fly pupae,” Rooijakkers explains. The parasitic wasp depends on the fly pupa. He drills a hole in the pupa and deposits his eggs in it. The larvae of the parasitic wasp feed on the larva of the fly. “This is how you are one step ahead of the adult flies.”
One comment. “If a barn has too thick crusts of manure, the pupae are not reached. It is therefore important to inspect the company first and to see which obstacles we may encounter,” Rooijakkers explains. “Removing a thick crust of manure can take up to a year. But that is also possible; there are good products available.”
You control 85% of the fly population during the first three stages. Rooijakkers: “If you still have flies after the first three steps, fly light traps inside or pheromone traps outside are a solution. But always tackle the problem at its source, then the costs are manageable, and you limit damage and nuisance.” An organic method of control is the use of swallows, for which the flies are the food.
APC’s advice is to start controlling flies in the spring. “This usually starts in week 12,” says Rooijakkers. “Start immediately with a preventive plan of fully organic control. After a year, you take stock and adjust the plans.”