Early-season hail injury generally occurs at the calyx end or on one side of an apple, because of the position of the fruits on the tree during this period. Later, when the fruits have become larger and heavier, they generally turn downward; so hail marks on well-developed fruits are more often on the stem end and on the blush side.
Fruits injured early tend to outgrow the internal condition produced, but they may become slightly misshapen as they develop. When fruits are struck by hail late in the season, the cuticle and skin covering the affected spots may or may not be cracked or torn.
Hail injury, late in the season, causes spots from 1/4 to 1/2 inch in diameter which become slightly sunken (see photo). The bruised flesh beneath the affected areas is usually brown, spongy and dry. Decay is usually not a problem following hail injury.
If the skin of the affected area is broken, this is definite proof of hail injury. Hail injury causing sunken areas with the skin unbroken, however, may be confused with the external appearance of cork spot (York spot). In a hail injury, however, the damaged flesh immediately below the sunken spot will be shallow and more or less follow the contour of the sunken surface. In cork spot the spongy, dead tissue is somewhat round or oval and may subtend the surf ace or may occur deeper in the flesh.