I had the same problem with my gelding, both this year and last year. The MTG also seemed to burn his skin so I immediately stopped using it. Last year I used louse powder and it seemed to work immediately. I just tried it again today so will see. I knew both times he didn't have lice, but maybe there is something in the powder that those "midges" or whatever they are don't like. Next year I am going to try washing his tail regularly with vinegar. I read somewhere that they did that in the old days, and thought it was worth a try.