This is what a bad case of cedar apple rust looks like. This my ugliest apple tree. The Yellow Delicious is especially susceptible to cedar apple rust. My next door neighbors have several cedars in their backyard which support a fungus that has little effect on the cedar, but can ruin a lot of apples. The most effective treatment is to remove cedars and junipers from within a half mile of apple trees. Since they aren’t my trees, that’s not an option.
I’ve tried sulfur and neem to little effect in previous years. And about five years ago, I tried grafting. I cut the trunk and tried a bench graft. My internet research did not lead to a successful graft. The Arkansas Black cuttings I tried didn’t take. Shoots grew from below, so I still have the Yellow Delicious. And it does produce.
I’ve found that if I pick off infected leaves that touch the fruit, the apples are not damaged. The amount of rust certainly impacts the overall health and productive capacity of the tree. But it isn’t a total loss. The other three apple trees in my yard are resistant enough not to have yellow spotted leaves. They are a Winesap, a Liberty, and an Arkansas Black. They are each more productive.
But could there be some advantage to all the yellow on the leaves? Could they camouflage the fruits from birds and squirrels? Not much it appears.
Something has been sampling at least a month before I’d consider them ready for eating.