Sunscald-Peeling Bark on Trunk

Have you ever noticed peeling bark on the southwest side of the trunk? Most trees and shrubs in the urban landscape are not native to the Front Range and are therefore at high risk for damage by Colorado’s seasonal cycles and climactic extremes. The common theme is lack of water along with quick changes of temperature and whipping winds.

Sunscald is a result of high altitude, low angle winter sun hitting vulnerable bark that is directly exposed to it on warm winter days. The sun rays hit southwest trunks and branches and heat them up causing the cambium layer to wake up and the “juices” to start flowing. Then as night falls and temperatures plummet the cambium and bark freeze, expanding water molecules, and cellular necrosis occurs. Reflection from light colored surfaces like snow, sidewalks, structures, etc. can increase the effect or cause it on other parts of the plant.

The most vulnerable trees are new transplants whose polar orientation has been changed leaving unhardened bark facing the Southwest exposure. Trees that are planted in areas that are much sunnier than where they originally grew are prone to sunscald since the bark was not conditioned for sun intensity. Sunscald occurs in the upper canopy when limbs are lost or removed that provided protection from the sun, exposing some inner limbs to a more intense heat.

Particularly susceptible species include Silver maples, Norway maples, Aspen, Honeylocust, Ash, Mountain Ash, Cottonwood, fruit trees, Birch and Willow. Once the damage is done the bark will often peel off, become sunken, discolored or soft and spongy.  Insects such as deadwood borers and earwigs will often move into the dead areas.

Tree wrapping from November through April is often a very practical and effective solution to this problem on young trees. Typically 2-3 years is enough for the trees to thicken and harden their bark in order to defend themselves without help. DO NOT LEAVE TREE WRAP ON YEAR ROUND as it can girdle the trunk. It is also a good idea to wrap trees that were previously damaged to prevent further damage.

Follow the link for more information on sunscald and tree wrapping: http://www.colostate.edu/Dept/CoopExt/4DMG/Trees/sunscald.htm