My Husband Was In Our Pasture For Only About 15

My husband was in our pasture for only about 15 minutes and came up with more than 30 ticks on his arms legs and under his clothes. We are planning to put horses in this pasture. Do we have to worry about ticks on the horses and if so, will Sevin sprayed on the trees and grass kill ticks or harm the horses. Thank you. C. Koelsch, YYYY@YYYY .