I have number of Maple trees, each around 4 years old. Lately their leaves have become a lot smaller with white mildew spreading out from the veins. They also have a green/yellow lichen on the branches which seems to be taking over the bark. I don't think the lichen is an issue but I am concerned that with the stunted growth it will completely cover the tree. I have 2 images if that would help you identify the problem.
Certified GKH Gardening Expert
Lichens and moss are generally not an issue on tree bark.
The white mold spots you discuss are likely a fungus of some kind. The fact that you have a number of trees effected can be of concern.
I would recommend a professional arborist inspect your trees for a proper identification and treatment coarse.