Sunscald is winter injury to bark caused by rapid temperature fluctuations. It occasionally occurs in mountainous areas and the high valleys of eastern California.
Identification
Damage develops after bark warms from exposure to sunlight and cools as the sun drops below the horizon. Young trees and trees with thin bark are most susceptible to injury.
Sunscald damage resembles sunburn of bark. Superficially similar damage can also be caused by boring insects, canker fungi, freeze damage, and mechanical injuries, such as trunks rubbed by tree stakes or hit by high-pressure sprinkler water.
Damage
Sunscald commonly discolors bark reddish brown, usually on the south and west sides of the trunk and limbs and on the upper side of poorly shaded horizontal branches. Bark then separates from wood, shrinks, appears sunken, and cracks and peels off in patches, exposing wood. Injured branches and trunks develop callus tissue, appear gnarled or rough, and may become girdled and die.
Solutions
To prevent sunscald, choose plants well adapted to the climate. Retain temporary, lower branches for several years after planting. Provide good cultural care (especially adequate irrigation). Apply mulch to moderate soil temperature and retain moisture.
Where sunscald is a problem, whitewash trunks and the base of main limbs. Tree wrap can be applied in cold climates to insulate bark from heating by sunlight; during the warm season, remove any trunk insulation.
