Losing hair .. Help

First off this is NOT my horse... this is the a pasture next to our home that a guy rents out to just about anyone... this horse is the only horse left on it.... he is losing hair badly on its face... we haven't had rain in so long I don't think its rain rot... he never gets any fly spray and only has tree's for shade... I would love to know what this is and if it is bad enough I am going to call a vet myself..

It's some sort of fungus. My horse gets it every summer. Just put some anti-fungal cream on there and it will clear up. If the horse will allow it's head to be bathed, a nice anti-bacterial shampoo will do wonders too.