I never have had much luck with oilers. I have tried them where cattle hang out in the trees, around the mineral, in panel gates to get water, but I still have fly problems. Seems like the "sock" dries out quick and then when they do use them there isn't anything left.
Anyone else fought these issues, or is it working and just hard to tell.
Of course in our swamp and irrigated pastures, it's hard to get good control on the flies with the ground being wet.
I usually just put them in the pens or have the dogs circle them up and spray ectiban on them.