Certain beetles called borers often attack fruit and ornamental trees that are weak or damaged by sunburn. Live cambium tissue beneath the bark can be killed by heat from the sun on the south to west side of a tree's trunk and on the top side of horizontal branches that are not shaded by foliage. Newly planted and young trees have thin bark which is easily damaged by sunburn. The trunk and major branches of newly planted and container grown trees should be painted with whitewash to protect the bark from sunburn damage.
You can use a commercial whitewash sold at some garden centers or make your own by diluting white interior flat latex paint with an equal amount of water. Also, irrigate as needed to provide adequate soil moisture for young trees. Wait until leaves and shoots are actively growing, then feed lightly with a fertilizer containing nitrogen. Scatter a small amount of fertilizer around the tree at least one foot from the trunk and water well to dissolve and carry it into the soil.
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension,