Does MLB have a dress code on the field?

I'm uming there is some kind of dress code...The Boston Red Sox with overgrown beards, pooka shells, hair extentions, doo rags, to me are pushing the envelope. Seems very cloppy and unprofessional to me. Manny Ramirez barely keeps his hat on. His extentions are well over his shoulders. All doo rag all the time. Looks terrible. I see it as an insult to MLB, the fans, and their team.