I can't see clear enough to be certain but quite likely powdery mildew, a common enough ailment on a lot of different plants at this time of year. Japanese maples are no exception.

It is far too late in the season to attempt any treatment now. Just allow the leaves to fall naturally but then clean up all of them and dispose. PM is primarily a cultural disease caused by climate and awkward or ill-suited growing conditions. Warm daytime and cool nighttime temperatures, nighttime condensation, dry, warm soils, overall humidity and poor air circulation all play a role. I don't recommend spraying for this disease as JM foliage is sensitive to all manner of topical sprays and typically develops a phytotoxic reaction. Tend to correcting any cultural issues, provide adequate sunlight and hope for the best. FWIW, PM on most woody plants is considered to be primarily cosmetic and of no lasting damage to the tree.

Planting a tree in the middle of one of the hottest and driest summers on record is not a great measurement of performance and certainly not a good indicator of what potential fall color could develop in coming years. Be patient :-)

And FYI, you may get more rapid responses and in-depth discussions if you post questions about your JM in the Maples forum. It is quite active (much more so than this forum) and has a good number of extremely knowledgable participants. Lots of JM afficionados hang out over there :-)

gardengal48,

Thank you so much for your response! This really helped me and relieved my worried mind. Thank you again for your input!

jml, you are very welcome :-)