What is causing this white grey , velveteen to the touch fungus on our Maple trees ? It has already destroyed one of the trees . I am worried that it has started on our 15 yr our Crimson King Maples. Can you give us some input? We live in the Ottawa Vally Region CANADA
There are several diseases that could be the issue.
This article list some of the most common.
I would suggest contacting a certified Arborist to inspect your tree.