Answer: Katsura is generally considered to be trouble free, so there is no common suspect to suggest and based on the information in your question I am not able to say what the problem is with any certainty. 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 to use and how/when is best to apply it. In the meantime, clean up any fallen foliage and dispose of it in the trash to limit sources of reinfection; also do a thorough leaf cleanup this fall for the same reason.
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