My 9 yrs. old grafted tree is in zone 6b. It started fruiting 5 yrs. ago. Three years ago after moderate pruning (unnecessary) I found black spots at the cut ends of the branches. Later found black areas in few leaves (like in your photographs) which I initially thought as related to the oozing from the pruning areas. Some or all of those leaves turned yellow and shed. Got worried. Later a colleague of mine told me it's from a caterpillar infestation. But I never chanced to see one there by then! Tree is growing healthy, 20+ feet in height now and skinny branches with full of fruits. Since we planted this tree for wild life we do not harvest. But have tasted in November, 5 years ago. Two inches round, mushy, very sweet and with 0 to 4 seeds. Probably zone 4 to 9 may be ideal for growing this tree which is it's natural habitat area. This may help.