Sunscald

Sunscald is a common problem found on young thin-barked trees. It is usually caused by a combination of environmental factors such as extreme heat, reflected sunlight, and dry conditions. We have had an uptick in the amount of sunscald seen in recent years. Just another increasing problem that we can associate with climate change.

Some people become alarmed when they see dead and missing bark on their tree’s trunk. They mistakenly think it is caused by a contagious disease that will kill the tree. With sunscald, the first symptoms of bark dieback are rarely recognized. Later, the bark may discolor with small vertical cracks developing along the margins, taking on a sunken appearance. Eventually small grey fruiting bodies (fungi) develop and feed on the dead tissues. They do not attack and kill living tissue.

How does it occur?

There are two kinds of sunscald, winter and summer. Both are caused by lethal bark temperatures exacerbated by reflected sunlight and drought conditions.

Winter sunscald is caused by bark temperature fluctuations. When temperatures rise above freezing, as can happen on a bright winter’s day, living woody trunk tissues thaw, losing their cold hardiness. When the temperature suddenly drops below freezing again, as can happen when a dark cloud passes over, tissue damage occurs. This bark tissue damage is commonly seen on the south or southwest sides of the tree’s trunk, especially when bright sunlight is reflected from a light-colored surface such as cement.

Summer sunscald occurs on bright sunny days from lethal sun exposure heating the bark. Moisture stress and reflected sunlight both exacerbate the problem. Damage occurs on the south or southwest side of the tree trunk.

Can sunscald be prevented?

Sunscald can be prevented by wrapping the tree trunk with a white or light-colored reflective wrap. These wraps are commercially available at local lawn and garden centers. The wrap is not necessary during the spring and fall months when the sunlight is beneficial. Apply it during the summer and winter months. In addition, take steps to prevent the tree’s root ball from drying out.

Will It kill my tree?

It all depends upon the degree of trunk damage, tree health and vigor. In time, an otherwise healthy tree will form what we call wound wood along the margins of the

trunk wound. This will be seen as smooth bark generating around the wound. As forms from year to year, it may eventually cover the wound. This is a positive sign. Some people refer to this as healing. As a tree ages, the bark will roughen and the potential for sunscald will go away.