Can someone please identify these strange growths on my Plum tree leaves. My tree leaves are infested with this and I think it is killing my tree. I've attached 3 photos. The trees are probably at least 20 years old. We have owned the property 10 years and they were mature when we moved in. We have two trees and they both have this problem, they are right next to each other. The "cottony" stuff you see in the pictures is just cotton from our Cottonwood trees.