Answer: Little bumps might be caused by blister mite feeding or could indicate an infestation of scale insects. The blister mite galls won't harm your plant to any great degree. In fact, they look kind of interesting. Scale insects can be pulled off with your fingernails. Curling leaves can indicate water stress, sun burn, or water stress. Without inspecting the plant I can't really diagnose the problem. You might want to take samples of the affected leaves to your local cooperative extension office or well staffed nursery for a more complete diagnosis plus control strategies. Best wishes with your maple tree.
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