Fruit of some apple cultivars tend to crack during the second half of the growing season. Sometimes cracking is limited to the stem end, and other times, the skin will split on other areas of the fruit surface. Cracking occurs most frequently during periods of high humidity following rains. Absorption of rain water through the skin, combined with the uptake of water from the roots, results in rapid enlargement of cells within the fruit. The internal pressure from the enlarged cells of the fruits creates a strain that cracks the skin. Severe cracking often occurs when heavy rains follow a period of drought. Fruit most likely to crack include those developing on the periphery of the tree canopy, those with high sugar concentrations, and those with skin russet. In the case of ‘Gala,’ there seems to be differential cell expansion within the fruit at the time of maturity. Cultivars most prone to cracking include ‘Stayman’, Fuji’, and ‘Gala’.
Rich Marini, Penn State University