how to get rid of gray moss from trees
How do I get rid of gray or gray black moss-like disease on trees and rhododendrons?
Certified GKH Gardening Expert
It sounds like you may be referring to lichen. Lichen normally does not cause any problems for plants, other than making them somewhat unattractive. For more info on lichen, and how to get rid of it, try this article: https://www.gardeningknowhow.com/ornamental/fungus-lichen/treatment-tree-lichen.htm