I also put Lavender on my hands and let my horses smell and I spray on the fly mask before applying. Peppermint is also very cooling and horses love it, avoid around the eyes and dilute the peppermint if putting directly on the nose. Do not spray mixture in the eye, ears or nose. You may place on hand and rub on but not in. If you do not have all these oils, that is okay. Make a mixture with water and oils of choice. Use 10-15 drops with 4oz. water if using a single oil. Apply every 3-4 hours or as needed. Every horse is different and my like different oils. The TerraSheild Blend works great as well. My horse loves Lavender and my other horse likes Peppermint.
Horses are sensitive so you can rub on hands first then let them smell your hands.
My horses are so happy. The flies were covering there fly masks. I felt so bad for them and was so happy I could provide them with some relief. I did not use Rosemary but it is suggested to use that one too, if you do make sure you dilute it.