Fruit and Nut Trees: Sunscald

Problem
Patches of bark on the trunk or branches darken and die. These patches appear on the sunny side of the tree. Cracks and sunken lesions (cankers) may eventually develop in the dead bark. Damaged trees have been recently transplanted or heavily pruned.

Analysis
When a tree is shaded by other trees or structures, or is covered with dense foliage, the bark on the trunk and branches remains relatively thin. If the tree is suddenly exposed to intense sunlight, the newly exposed bark and the wood just beneath the bark may be injured by the sun's heat. This frequently happens when young trees are moved from a shaded nursery to an open area, and when trees are heavily pruned during periods of intense sunlight. The problem also occurs on cold, clear days in winter, as cold bark is quickly warmed by the sun. The damaged bark usually splits open, forming long cracks or cankers. Decay fungi may invade the exposed wood. Sunscald is most severe when the soil is dry. Young trees may die from sunscald.

Solution
Unless the tree is very young, or extremely damaged, it will usually recover with proper care. Water and fertilize the tree to stimulate new growth. To prevent further damage, wrap the trunks and main branches of recently pruned or newly transplanted trees with tree-wrapping paper. Or paint the exposed bark with a white interior latex or whitewash. The tree will eventually adapt to increased exposure by growing more foliage and producing thicker bark.