Hi, This is happening on two trees I picked up from a N FL orchard. Leaves are turning yellow with just a few green spots remaining prior to falling.
For the first month or so all was well now about 10% of the leaves are having this issue. Also, new plum trees I purchased at the same time are much worse off. Leaves look almost the same.
Look up Marrsonina Leaf Blotch.
I think your tree has it.
Google says it does look a lot like it, and we have had wet weather. Funny that leaves seemed to go from green to like the pic I posted without any of the intermediate stages. I have copper fungicide but none of the others. Have to do some research unless someone here has had success fighting it…
For reference, here’s an article from Penn State about Marssonina:
The article says that MLB typically shows up in late summer. I suppose it might appear earlier in N Florida?
Yep! June in SW GA / N FL = August in PA 
I have them for the past few years. I am in zone 6a. By late August, leaves dropped en masse. By Sept, my apple trees barely had any leave left on the trees.
Thanks to @alan who brought this issue to our attention. I think Alan also gave us the solution. Last year, I sprayed it with the mixture of myclobutanil and Captan in the summer twice. It really helped. Hope to do it again this year.
I had it two years ago. Almost all leaves where gone in September. Sprayed last year as @mamuang mentioned and the apple trees where OK.
Thanks everyone for your help!
