If you think it's fungal use an anti-fungal (like lotrimin etc.) not an antibiotic. Though looking at it I wouldn't be surprised if you had both things going on--a primary fungal issue with some secondary infection that may need antibiotics. It's hard to tell from the pic. but I would start by bringing the bird in and cleaning the comb area up with warm water. Hopefully some of the crusty stuff will loosen up and you'll be able to get a better idea of what you're dealing with.