Symptoms of black rot on an apple, being caused by the plant pathogenic fungus Botryosphaeria obtusa (image : Clemsen Univ.)
Above is the fruit phase of the disease. If you see this you should be on the lookout for cankers on the trunk. The first appearance will likely be on the leaves as little spots. This phase is know commonly as frog eye leafspot, so called due to the double circle reminiscent of, well, a frog’s eye.
Can be managed organically, but like most tree fruit diseases, keeping the orchard clean of old infection, rotten infected fruit and the like will go a long way in making this stinker more manageable. Remove all infected prunings from the orchard area.
As with all fungal diseases, it is prudent to allow good air circulation in the orchard through timely pruning. Since most pathogens require a wetting period to become established, and certainly for quick spread, this moist conditions in the canopy should be kept to a minimum. Airflow and access to direct sunlight will help keep disease cycling to a minimum.