Basic Info:
Sun can be a tree's best friend or, under adverse conditions, an enemy. At some times of year, it can cause sun-scald cankers on the stem or trunk and large branches of many hardwood trees; hardwoods are those trees that lose their leaves in winter. Sun-scald occurs during both winter and summer when portions of the cambium are killed due to temperature stresses; the cambium is the very thin layer of cells directly under the bark through which the water and nutrients flow between leaves and roots. Kill the cambium and the bark over it dies and falls off. Trees with thin, dark-colored bark are especially prone to this damage. Summer sun-scald is heat injury to the exposed bark during the summer months. The bark will die and a canker forms around the damaged area. The wound or cankered area is an excellent location for decay and other harmful fungi to enter the tree and cause further damage or permanent defect. Winter sun-scald is an injury from rapid changes in bark temperature during cold sunny winter days. Exposed darker bark becomes much warmer on the sunny side of the tree than the air temperature during the afternoon, but cools very rapidly after sunset. These temperature changes can result in bark injury that can also result in canker formation. Both summer and winter sun-scald injuries tend to occur on the south to southwest sides of the tree. That is because this is the direction from which the warm afternoon sun comes. Trees are most susceptible when they are growing in the open, when nearby trees or structures are removed causing new exposure, or when they are moved from a shaded nursery or other location to an exposed site. Sunscald is rarely fatal on their own as a vigorous and mature tree will compartmentalize the damage and heal around it effectively. The problem with these injuries is they are usually exploited by parasitic insects, birds, fungus, and decay.
What We Recommend:
1) To help prevent these damages the trunk can be covered with various types of material that help insulate the trunk from temperature changes. Dark colored covers are not advised as they will make the temperature changes more drastic. Be sure to monitor the cover over time as they can girdle the tree, house insects, or encourage decay if it holds moisture. Adjust or replace as needed.
2) Protect the base of your trees from direct sunlight. Many trees naturally do this on their own but planting shrubs or other plants around them can help shade their exposed base. A shaded base will also be less inviting for parasitic insects as most boring species in Alberta seek trees with direct sunlight where they infest so they don’t freeze to death over the winter.
Trees Effected by Sunscald: Young Ash, Poplar, Aspen, Fruit trees, Birch, Mountain Ash, Amur Cherry.
Government Informational Source Link: https://tidcf.nrcan.gc.ca/en/diseases-caused-by-pathogens/factsheet/1000135
