Clean the coop, is the short answer. You want to eliminate any manure laying around for them to lay eggs in or whatnot. You can also use D.E. in the coop and run to kill any of the eggs and maggots.
I use a lot of DE. It helps to cover up the odor but you have to keep the coop clean, I use hay for the floor of my coop its easy to rake up and put in the garden and I cover the nests, coop floor and roost with a heavy layer when I change the hay, they have something I think its called stall dry that I have heard works great to, good luck, summer hasn't gotten here yet and the flies are already a problem, I wonder what aug will bring marrie
I totally understand what your going thru. I am a newbie and the flys in the coop and run was horrible. I ordered DE off ebay( they had alot of good feedback) make sure its food grade and within a couple days the fly problem was solved. just sprinkled in coop and run. worked perfectly!
Listen, I haven't tried this. I remember so one posting this....... take a 2 litter bottle and put apple cider vineger with dish detergent about a 1 of water to the bottom. That is all I can remember so I hope they will post it again because I'm going to try them all