Fly control is a multi pronged attack,
1. Step one is manure control , You must have a manure management plan. That means NO manure in the pastures, or manure piles to provide breeding grounds.
2. Fly predators, spalding labs fly predators work great,
3. Fly traps. The right kind of fly traps, any of those add water or scented ones are the wrong type, you want the biting fly traps. These are live blood aaters and arnt attracted to those scents, they may look similar but those bait traps are just luring in garbage and house flys from other areas, and not the ones biting.
4. You horse specific techiniques, sprays and sheets.