Our light intensity is very strong in the desert. Some thin barked trees and shrubs get sunburned if they don’t have enough protection from strong sunlight. The natural way to protect 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 encourage sunburn.
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| Sunburn, like on this ash tree, starts out as a discoloration of the wood. |
Plants that typically sunburn include many of our fruit trees, mostly peach and apples. Ornamental trees and shrubs also get sunburn. Plants that I see with sunburn include Japanese blueberry, locust trees, ash trees, Indian Hawthorn, and others.
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| Sunburn can happen to fruit, too. This yellow apple has the first sign of sunburn on the fruit facing the sun. |
Severe sunburn causes the plant to die on the side exposed to the sun. Bark on this side is loosely attached to the trunk. When you pull this bark away from the trunk you may see oval-shaped holes in the wood. These are exit holes of borers. Removing the bark also removes hiding places and birds have a better chance picking them off when they emerge.
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| The side facing the sun dies under severe conditions and boring insects can invade the living parts on the edges of the damage. Eventually this becomes part of the tree that dies. |
Having rock mulch around plants that do not like rock mulch 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.
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| In the case of sunburned fruit the area darkens as the sunburn worsens. |
What’s the problem with sunburn? When humans 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 damage. The borers create more leaf loss which increases sunburn. At this point the plant falls into a death spiral.
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| The side of the branch or trunk facing the sun has the most damage. In this Bottle tree it is the upper surface of the limbs. |
Use surface mulch, particularly wood chips, and not bark mulch. Don’t water trees and shrubs daily. 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 they receive water, it should water the roots to a depth of at least 12 and preferably 18 inches.
