Disease on Bark of Acers
White cotton wool-like small scales presenting on bark of our acers. Please advise of causes if pest and best treatments.
This could be Mealybug, Wooly Aphid or a fungus.
Also sometime lichen can have a white appearance. Lichen is harmless to the tree.
I would treat with Neem Oil. It works as both an insecticide and fungicide so that you are treating both possible problems.
Here are some links for you.