Rain Rot?

Definitely rain rot. Scrub daily using a curry comb and anti fungal shampoo. Then spray with Muck Itch. It cleared up in a week for me:)

Definitely rain rot. Scrub with curry comb and anti fungal shampoo daily. Then spray Muck Itch on it. It cleared up in a week for me.

Oh OP another thing. Clean your brushes after use. Plain soap and water or put some betadine-scrub in a bucket and use that (probably better idea since that's safe for horses.. some soaps are not.)