Now is the time to prevent sunscald damage on trees

Sometimes known as “southwest injury”, sunscald on trees is damage to the bark on the side of the tree facing the sun, which in our area is the southwest.

Sunscald can occur in both the summer and winter time and be caused by many environmental factors. Sunscald is identified by the bark on the trunk and lower limbs cracking and the bark dying, with dead brown wood being exposed after the damage occurs. This sunscald damage can be an opening into the tree for fungal diseases and insects to start to infest and hurt your tree.

Sunscald damage happens in a few different ways. In our area, the damage is primarily done in late winter (February to March) when the south side of trees will warm up from the sun during the day, causing the fluid in the bark to start flowing, and then as evening arrives the temperatures drop dramatically and this fluid freezes and damages the bark. There may be several episodes of thawing and freezing within a winter that can create this damage, but ultimately the temperature fluctuations can have a negative impact on the tree.

Most of the damage occurs on the trunk, while sometimes damage can occur on the lower branches as well. Sunscald can also occur during the summertime when trees are topped or heavily pruned exposing bark that had previously been shaded from direct intense sunlight. Planting trees that had been in a semi-shaded nursery into a full sun scenario can induce sunscald, as well as planting trees next to a light-colored pavement which reflects both heat and light onto their bark can cause this problem.

There are several methods to protect your tree’s bark, depending on the setting your tree is in. In many fruit orchards where this is a problem, trees have their trunks and larger branches painted white. This reflects light off of the trunk, therefore reducing the warming effect during the late winter/early spring, and prevents the fluids in the bark from fluctuating from warm to cold as drastically.

If you choose to paint the trunk and larger branches of your tree, use only a white interior latex paint. Other types of exterior paints contain ingredients that can be harmful to trees. You want to paint the trees after the foliage has fallen to the ground and only from the bottom branches to the ground. Trees that are used for ornamental purposes should not be painted as it detracts from the beauty of the tree.

In the case of ornamentals or a home orchard that you do not want to paint, consider using a burlap wrap, paper tree wrap, or a flexible plastic wrap material around the trunk of your tree. This protective wrap will block the sun, and protect your tree. A more durable option, but more costly, is using 4- to 6-inch diameter flexible PVC pipe as a covering around the trunk of the tree. To do this you cut down one side of the PVC pipe and drill holes in the top and bottom so that after putting it around the tree it can be tied on the top and the bottom so that it does not come off.

The best step in preventing sunscald is to plant trees that are resistant to this type of damage. The other key to remember is to make sure that trees have an ample water supply going into the winter. Too often a tree that normally doesn’t struggle with this issue, may start to have problems because they went into winter dry, and then as moisture reaches their roots in early spring they take it up as quickly as possible, and their bark become full of fluid right at the same time the temperatures are fluctuating.

The temperature fluctuation between warm days and freezing nights mixed with a tree pulling up lots of water could cause ice crystals to form under the tree’s bark, and therefore cause damage.

For further sunscald questions, please feel free to contact Lance at (208) 624-3102.