I second the diesel permectrin mix poured onto a rub. 

In some locations I string the rub across a lane to water. In one summer pasture I didn't have a lane so strung the rub between a tree and post near the waterer. Here's a recent picture of this rub. It works, once the cows figure it out. My cows have been using these rubs for a couple years and generations. They will at times come over and wait to use it when they see me coming to douse it with my red gascan full of diesel/permectrin mix. 5 oz of permectrin in 2.5 gal of diesel is how I mix it most of the time.

Cows and calves have figured out it helps and will come over and stand under the rub as you can see from the soil worked under it. Calves rub their heads on the rub.  I thought IGR etc only helped reduce new flies from hatching in the manure but doesn't due anything for flies already there or that cone in from a pre IGR pasture or a neighbors place.

At another location I had a case of pinkeye and put fly tags in all the cows when my vet treated the one. The tags in addition to the rub over there stopped the pinkeye from spreading to other cows. This is a location near a couple other herds which may explain why more pinkeye fly pressure there. This is the first time I've had to use the fly tags recommended by my vet.

(IMG012 heifer at salt block and fly rub 082516.jpg)

IMG012 heifer at salt block and fly rub 082516.jpg (155KB - 64 downloads)