The cause of the splits is invariably irregular watering. When the tree suddenly gets a hefty drink following a period of drought, the apples quickly expand, which often leads to the skin cracking. The fruit usually produces a corky, scab-like covering, but in the case of mature apples the split can lead to rotting.
Shallow splits start to appear on apples, which are then covered by a corky scab. This can result in further problems, as infection gets into the splits and leads to rotting.
After a spring watering, lay a thick mulch around trees to help preserve moisture in the ground. Make sure they get a regular drink, especially during a long drought and when they are thick with apples.