Preventing sunscald in young trees

When examining a young tree that is having major problems with cracking on its trunk, or possibly even losing bark, I often blame the initial cause of the problems to sunscald. Sunscald usually occurs when the tree is very young, with thin bark. It is most commonly seen on the southwest side of the tree, but can occur anywhere the sun can hit it.

Sunscald damage normally occurs in the winter, when the tree is subject to frequent freeze/thaw cycles. Think about it… you have a nice sunny January day, and the sun warms up the trunk, perhaps thawing it out. Then what happens that night, if the clear skies continue? The mercury heads for the bottom of the thermometer, and everything re-freezes.

This constant freezing and thawing damages the bark, and a crack may develop which eventually widens and exposes the wood underneath the bark. Needless to say, this is a bad situation. If the tree is healthy and vigorous, some healing may occur. But often the damage is permanent.

Trees that are most susceptible to sunscald damage have smooth, thin bark. These include most fruit trees, but also ornamental species such as maples, willows, oaks, and many more.

The key to sunscald prevention is to reflect light. In some places, people will paint the lower trunks of susceptible trees with a thin coating of white latex paint. Be sure it’s latex paint, if you decide to take this approach.

The high-tech way to reflect light off the trunk of the tree is to use a tree wrap. The best kind for this purpose is the expandable white plastic type. This not only reflects light, and keeps temperatures cooler on the trunk of the tree, but it also offers some protection from nibbling animals such as mice, voles, and rabbits.

Late fall is a good time to put tree wrap around trees you wish to protect. It’s best to remove tree wrapping materials in the early spring. March would be ideal. If left on the tree, these wrapping materials may girdle the tree if they are too tight. The expandable tree wrap may prevent this to some degree, but I still think it’s a good idea to remove it every spring.

There is good news. As trees age, and develop thicker bark, they are less subject to sunscald. Therefore, as a thicker bark develops, you usually won’t need to be putting tree wrap on your tree each fall.

University of Missouri Extension programs are open to all.