Some thin barked trees and shrubs will get sunburned if they don’t have enough protection from strong sunlight.
 |
| This reddish-brown discoloration is sunburn. In the first stage of sunburn we see the beginning of death onsides exposed to the South and West |
Plants that typically get sunburn include many of our fruit trees, mostly peach and apples. Ornamental trees and shrubs also get sunburn. I get a lot of pictures of sunburn sent to me with sunburn and include Japanese blueberry, locust trees, ash trees, Indian Hawthorn, and others.
 |
| This is the trunk of an ash tree on its west side. It first got sunburn. After sunburn the borers attacked it. What you see now is loose bark covering dead wood killed by borers. You can take your fingers and just pull this bark off of the trunk easily. You should do it anyway. You will not hurt anything. That site is already dead. The tree is still alive because the trunk is alive on the other side of the tree. |
The natural way to protect these plants from sunburn is to allow these plants to shade their own trunks and stems with leaves. Not providing enough water can thin out the canopy of trees and shrubs and encourages sunburn.
 |
| When you pull this bark away from the trunk you will see oval-shaped holes in the wood. These are exit holes of the bores. Removing the bark also removes hiding places and birds have a better chance picking them off when they emerge. |
Having rock mulch around plants that do not like rock mulch also reduces the number of leaves and increases the chance of sunburn. Plants that do not like rock mulch, like the ones I mentioned above, will develop an open canopy, leaf loss, and sunburn.
 |
| This is sunburn on a bottle tree. The leaves drop from the canopy and expose the trunk and limbs. High sunlight intensity causes sunburn once the leaves are gone |
What’s the problem with sunburn? When we get sunburn we recover. When plants get sunburn, particularly in a desert climate, they frequently decline and die. Attack by boring insects, or borers, is the first phase after sunburn. The borers create more damage and more leaf loss and more sunburn. After that, the plant falls into a death spiral.
 |
| Sunburn caused the top of this Japanese blueberry to die. Then the top had to be removed and it was pretty ugly. Japanese blueberry should not be in rock mulch. They should have wood chips around them. |
Use surface mulches particularly wood chips and not bark. Don’t water trees and shrubs daily but water them two or three times each week during the heat of the summer. Reduce the number of times per week during the cooler months. When you do water, give them adequate amounts so that the soil is wet to at least 12 inches and preferably 18 inches.
