The last few years flies where bad for me too and I was determined to make a dent in them this year. So far this year I would say I have reduced the fly population by 75%. In the early spring I put out tubs with IGR, these seem to only work for awhile. I then started spraying with permethrine and pro late using water and a bit of mineral oil usually every 3 to 4 weeks. I rotated the chemicals using permethrine one treatment then pro late the next. I will also be rotating the cows to different pastures several times over the growing season spraying them before the move so they are going to a clean pasture and not bringing flies with them. The cows seem to be a lot more comfortable this year.