Is this Favus? How do I treat this?

To me, that looks more like some scabs caused by Fowl Pox or an infected area due to a fighting injury. In the case of Fowl Pox, the scabby area should dry up and heal within 2-6 weeks. There is nothing you can really do to treat Fowl Pox, since it is a viral disease. The only thing you could do is treat with antibiotics to prevent secondary infection.

In the case of a fighting injury, I would apply some antibiotic ointment to the area once or twice a day and see what happens. Make sure you don't use any ointment containing any "cain" or "caine" ingredients, since those are harmful.

 

I agree.

Also, some of my birds get dry combs when it gets cold out. It's possible that the whitish yellow is dry skin flaking off. I haven't yet found the reason why it happens to my roosters, but by putting a moisterizer like antibiotic ointment on the combs, it goes away almost immediately.