I have noticed the flys have become resistant to the Tri-Tec here. We also tried Bronco and it didn't do a darn thing.
I sprayed the boys with it again this morning and everything was fine. I really think the swelling in my hand was due to the stress of trimming those huge feet! Lol.
I do notice a difference now that I am using this spray. The horses don't stomp nearly as much and they seem more comfortable. I think it smells good, too! I'm giving it a thumbs up! :)