Autumn Blaze Maple Leaf Problem
Thanks for the question.
What you are seeing are maple galls. Such galls are not harmful to the trees and will fall with the leaves this coming fall. For more information see:
These galls are the result of small mites that laid eggs on the leaves earlier this summer. These eggs hatched into small larvae that are now residing within these galls. From these larvae adult mites will soon emerge. These adults will over-winter under the bark of the trees
The following three sites will give you additional information on this mite together with possible control procedures:
Thanks for using this forum.