Looks like bud rot, or some really bad budworm damage. I vote for budrot. as for how to treat it all I know is that its a mold I think? I've never had to deal with it, but I would recommend cutting off that bud and getting rid of it and then finding some kind of antifungal spray. nnem might work, I'm not sure though. Maybe someone who's encountered this will be kind enough to reply.