The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: The apples from my apple tree are all crusty and cracked. What caused this? How can I prevent it from happening again next year?
Answer: Your apples probably have a disease called apple scab, which is one of the most common diseases of apple and crabapple in the United States. is caused by the fungus, Venturia inaequalis. Although you noticed the disease on the fruit, this disease caused spots on leaves earlier in the season.
Management of apple scab involves a combination of steps: planting resistant varieties, raking and destroying fallen leaves infected with the scab fungus, pruning apple trees in late winter to "open" the canopy, and using fungicide sprays for susceptible apple and crabapple cultivars.