I was just commenting on my local forum, about how bad the flies are.
We never have much of a fly problem but I am getting bit by house flies, already! That never happens until Fall, when they know they're about to die off.
Deer flies are early and there's a lot of them. Fly spray doesn't help once the horse starts to sweat --- you know nasty run down the sides sweat --- with all the humidity
As I type this at noon, we sit at 84 F with a heat index of 88F; humidity is 62% and the dewpoint (which is the killer) is 69.8% Blech, a thousand times blech
I have never used Fly Predators because we use weed killer around the fences and the workshop, which is 30 feet from the horse barn.
I have read any kind of "killer" stuff will kill the Fly Predators.
My best suggestion is to keep your horses off sweet feed if they're on it, as it permeates thru their sweat and only makes the fly situation worse.
Keep them showered down at night, if you possibly can. I shower my horses every morning or night but I don't shampoo them. I just knock the sweat off them with cold water and a wash cloth.
Keep the weeds cut down on the fence lines and around the barn, as much as you can.
Lastly, hope Fall gets here quick