What you have is probably a lichen and not a fungus. There are many lichens in Maine. I have them on Maple, Oak and Apple trees with no discernable harm in the Midcoast. This link should help you determine which lichen is on your Azalea and other shrubs

Here is a link that might be useful: USDA Durham NH Field Office Publication

Thanks for posting that, frontporch. Interesting. I love lichens, tho I don't know anything much about them. In fact, I encourage their growth by trying to keep things damp and spraying rocks with Miracle Gro--takes a long time but it seems to help. I don't know if lichens can become a problem to a plant, such as kennebunker reports, but hope someone has that answer.

Lichen.....I knew there was another word, just couldn't think of it, thanks.
I googled, seems that there's nothing that can remove it from trees and shrubs. It's not supposed to do any damage, but that azalea just looks ugly covered in the stuff.
I wound up pruning the shrub way back. It had gotten a bit lopsided anyway. I've forgotten the variety, it has lovely red blossoms. Its roots were damaged by mice or something one winter, or so I was told. Its twin failed to revive. I moved this one to another spot and it looked quite nice til it got lichenized.