The funny thing is the feed companies and university people cant establish how far a fly can travel. I know of guys that swear by IGR. Especially if you start using it early enough. It kills the larva, not the flies. Also 1 type of the 3 types of flies. Then you go to an extension meeting and hear that your neighbors neighbor has to feed IGR for it to work. That is why I spray instead. I can get them all. Time consuming PITA....ya sometimes. Do it on a day when the wind is right and corner them around a tank or something its not too bad. Its amazing just how few of flies can cause a weight loss. Also them flies add up quicker than you think. Seen UNL pics where they have counted them.
UNL is doing some research about flies being attracted to the color blue. Medium to dark blue. Soak that color of material with atraban or what ever and hang off the side of a windmill etc.