Greetings Smokey, Welcome, you didn't mention where you are so the folks have an idea how damp or dry your area is. But you could give us a closer look so the people here can descide if it is: Fungus, mildew or scale insect.
It looks to me like like Letchen. I have trees that have letchen growing on the bark or branches, it doesn't seem to damage the trees but does grow on cancled branches.
Give us a closer picture so we can make a clearer judgement. Thank