Applying white paint to trunks (whitewashing) reflects light and reduces bark heating, thereby helping to avoid sunburn. Wood-boring pests, especially flatheaded borers, are frequently a problem on trees where limbs or trunks have been sunburned.
Sunburn often occurs on the stems or trunks of young woody plants. Their bark is thin, and they may not tolerate being exposed to direct sun in landscapes.
Older trees can be damaged when bark is newly exposed to the sun because of pruning or premature leaf drop. Removing structures or trees that provided shade or adding pavement or structures that reflect light or radiate heat around established plants can also lead to sunburn. Anything that makes roots unhealthy or prevents plants from absorbing adequate water may contribute to sunburn.
Apply white interior (not exterior) latex paint, diluted with an equal portion of water, to the trunks of young trees and to older bark newly exposed to the sun if it is susceptible to sunburn. Interior water-based paints for whitewash are safer to trees than oil- and water-based exterior paint.
For more information, go to ipm.ucanr.edu