Malus Red Splender Crab issue
We planted the tree about 5 yrs ago. Out of the 5 yrs, probably 3 of them, we have had leaves develop these spots and turn brown and drop quite a large amount. I’m assuming it’s some kind of fungus? I’ve tried spraying, and using a systemic but do you have to wait to the beginning of the season to do it? When the blossoms are out and then following, it looks very healthy. We've been told to pick up the leaves as much as possible to prevent a continuation of the problem.
I wonder if your crabapple has cedar apple rust. Is your tree in proximity to a juniper or cedar tree. See this info from Clemson University: http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2000.html