Did you think only you could get sunburn? Your trees can, too. It’s not a common problem in our area, but it does occur. It’s caused by the same conditions that sunburn us – sudden exposure to high heat and intense sun rays. Drought stress can also contribute to sunburned trees.
The big difference between our sunburn and that of trees is the amount of time it takes for symptoms to show up. We turn red immediately, but it takes awhile for trees to exhibit any symptoms.
Sunburn usually occurs on young trees and thin bark trees, especially those with dark bark. Sunburn damages the tissue just beneath the bark. The bark discolors and dries out, cracks and starts peeling off. These symptoms are quite similar to those for sunscald. However, sunscald occurs in the winter and is caused by freezing. Thus the more common name – frost cracking.
In addition to drought stress, sunburn can be caused by sudden exposure to the sun. This can be caused by removing nearby shade, such as other trees or structures. If you are planting new trees, try not to plant them in the heat of summer. Otherwise, take special care to protect them until they become established.
Protection measures start with watering. Be sure the tree receives one or two inches of water a week. Also, mulch and compost around the base of the tree. Organic mulch and compost will help the soil retain moisture and lower the soil temperature.
Wrapping the trunk is another protective measure that I use very cautiously. Wraps include paper, cloth and even painting the trunk. The method most arborists, including me, prefer is to loosely wrap the trunk with light colored window screening This type of trunk guard reflects light, while allowing air and water to reach the bark.
Tree roots are intended to keep the “plant” in its place. Thus, trees do not react well to environmental changes. Sunburn is one environmental change that we often don’t think of, but the results can be very devastating. However, sunburn can be prevented or treated. But prevention is much more effective than treatment. So, consider the effect on a specimen tree before removing the shade that has contributed to its good health for all these years.