Doesn't look like disease or insect damage. Instead, something was perhaps sprayed on it? In any event, very unlikely to get worse.

Thanks Jean. Should I remove affected leaves or prune a bit as usual in the fall? BTW, unfortunately, I couldn't load the image you posted even when i copy-pasted the url. what was it?
Thanks again,
Dory

I'd let things be. The leaves will soon drop of their own accord because it's time. No point in removing leaves that aren't diseased.