Answer: I apologize if you receive a duplicate answer, the system seems to be glitching a little bit as I just sent out an answer to your question but it has reappeared. Based on the information in your question I am not able to make a diagnosis; there are no "usual culprit" diseases with this tree because it is generally considered to be quite pest and disease resistant. I would suggest you consult with your local Cornell cooperative extension to obtain a specific diagnosis and based on knowing that, determine how to proceed. If a chemical control is needed, they will have the most up to date information on what ot use and when/how is best to apply it for maximum results. In the meantime, clean up any fallen foliage/twigs and dispose of them in the trash to try to limit sources of reinfection; do a thorough clean up this fall for the same reason. I hope it is nothing too serious.
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