Back, I am not sure how close your manure pile is to your barn but be careful spraying your stalls and such if you use predators. You do not want to kill off your helpful little predator guys by accident.
I have a biting fly trap, that helps with the green heads and deer flies. I have a fan outside under the over hang that keeps the air under the over hang moving all day. They have individual fans in their stalls (which they have access to in the evening and over night).
My manure pile is about 50 ft or more from the stalls. I have worried about it though I can not off the top of my head remember what distance they had on their website. I do remember them saying that if you put the predators in the stall to take the horse out of the stall before spraying, so in my mind if you just take the horse out of the stall to spray then that is just a few feet away from the stall itself.