Last year the horse flys were just awful. I tried all sorts of home remedys because I felt I was overdoing it with the pesticides.
I acually mixed up a concoction of ac vinagar, garlic, a leave in human conditioner and a bounce drier sheet in a bowl strained it, cut it with water and sprayed it on my horse. She smelled pretty funky but it did work.
I also mix a gloppy mess of bees wax and pine tar, melt it on the stove and put it on their hooves with a paint brush when its been really wet.
I use ac vinagar for a lot of things even on myself.
I also found a "recipe" for fly spray that I used last year. It was equal parts vinegar and dishwashing liquid(like dawn) and then a lot of water. I agree that it definitely smelled funky but seemed to wok well. I also use a lot of human shampoos and conditioners and detanglers when bathing.
I have a homemade whitening paste. All you do is mix one part hydrogen peroxide, one part milk of magnesia and enough cornstarch to give it the consistency of elmers school glue. You put it on any white markings and brush it off the next day when it's dry. I have yet to use it on my horse but I use it on show dogs (samoyeds) all the time and they need to be extra, extra white for the ring and it works. Heavy stains will need more than one application. How many depends on the stain. And it won't hurt if ingested. The younger dogs eat it sometimes and they're always just fine. The milk of magnesia might cause some diarrhea, but that's what it's supposed to do, so no big deal.