A: First, do you know what kind(s) of flies are bothering your horses? How do the horses respond when attacked by the flies? This fact sheet illustrates the main kinds of flies we have in Minnesota.
Fly Predators kill house flies and stable flies, but not other kinds of flies. House flies and stable flies develop as maggots in moist, decomposing organic matter, such as accumulated horse manure, soiled (wet) bedding, and spoiled feed (hay or grain).
I recommend people do the following to prevent flies from building up to annoying levels:
- Dispose of accumulated waste in spring, so flies have little to develop in when weather warms in June.
- From June thru September, spread manure daily, keep bedding dry, and keep feed from getting wet and decomposing.
You might also ask if the flies bothering your horses could be coming from neighbors? Flies will travel a half-mile easily, and flies could be coming from other stables or livestock facilities. If your neighbors are a source, then all you can do on your place is spray residual insecticides to kill the adult flies. Source reduction would require your neighbors to improve their debris management, and maybe Fly Predators would be of help there.
By Roger Moon, PhD, University of Minnesota Livestock Entomologist