Have not seen anything be a foliage problem on Yellowwood, it always seems to be a root problem with these. That said, as a general rule foliage disease over-winter in leaf litter, just as you suspect. So while that may not be the case with this particular organism, it certainly is a good place to start. That leaf litter either needs to be then removed to a remote location (i.e. trash to the dump), or burned. I would not try to compost it, as some of any innocullum that might be would likely survive. I personally would burn it, then redistribute the ash (since the ash is high in minerals). Might also be wise to spray the tree with copper sulfate again just before you have seen the disease appear the last couple years. In fact I would follow this regimen for 2-3 years in an effort to eliminate as much of the organism as possible.

And for the spraying chemicals and poisoning the earth crowd, copper sulfate is a natural chemical compound that occurs at some level in most environments. In addition it's use is widely approved by most organic farming organizations. Now that does not mean use it to excess, just that is is safe and useful short lived treatment. Educate yourselves.

Arktrees

Thanks very much arktrees. I needed someone to verify my understanding of this fungal disease and treatment. And give me a little nudge toward the rake.

Just out of curiosity could you share a picture?

What you explain sounds nothing like powdery mildew. Yellowwood is not effected by this either from what I've read.

I wish I could, whaas, but I have neither the camera nor the skill to upload a picture. To me, this looks more like sooty mold if there's such a thing as dark red sooty mold. But there are no insects involved at all. So, as I said, the arborist and I arrived at powdery mildew by default. What I do know for certain is that it was contained by the copper sulfate application.