Newly planted trees could fall victim to sunscald

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The first day of summer is quickly approaching on June 21, and the warmer temperatures are definitely a welcomed sight from the cold winter temperatures we experienced earlier this year.

However, with these warm temperatures, we begin to see the development of a type of injury on newly planted trees that is actually a result of the cold winter. This problem is called sunscald.

Sunscald is not only disfiguring but often leads to a long, slow mortality spiral. It usually appears only on the south or southwest side of trunks and only on recently planted trees.

The first indication is a small vertical crack in the bark. These cracks often run from close to the soil line up to the lower branches. As the crack opens, the bark begins to peel back, exposing the wood and allowing fungi to attack the xylem and insects access to the open wound.

Sunscald is a result of the damaging of the cambium of a tree, which is the layer of actively growing cells that create xylem and phloem — the tissues that take up water and nutrients. Though the air is well below freezing, the intense winter sun warms the thin bark and the cambium below it. This typically occurs in late afternoon when the low angle of the sun results in sunlight hitting the trunk directly.

The intense sunlight causes the cambium cells to start dividing. As a cloud moves across the sun or the sun sets below the horizon, the trunk quickly returns to sub-freezing temperatures, causing the cambium to freeze and die.

As a result, trees can no longer move water and mineral elements from the roots to the foliage nor supply the roots with sugars and other organic chemicals necessary for growth.

At best, trees stressed by sunscald will reestablish more slowly and are more susceptible to diseases and insects. While these trees may ultimately survive, replacement trees outgrow severely damaged trees, so consider replacement.

Sunscald is almost always limited to young, recently installed landscape trees. It is not seen on mature trees or those in forests. It is most common on species with thin bark than trees with thick or exfoliating bark.

Problematic species include Maple (Acer spp.), Linden (Tilia spp.), Pear (Pyrus calleryana), Crabapple (Malus spp.), Cherry, Plum (Prunus spp.), and Willow (Salix spp.)

Install trees with larger soil balls (containing more roots) and water during the winter months to help prevent water deficiencies leading to sunscald.

Sunscald can also be prevented by shading the trunks of young, newly planted, thin-barked trees.  A double layer of plastic or fiberglass windowscreen is an easy and economical way to accomplish this.

Wrap the double layer of screen around the trunk.  Hold the two ends of screen and staple them together (not to the tree).  Leave excess screen to prevent girdling damage to the tree. This protective covering should be removed after the tree begins to become established, usually one or two years.

For more information on sunscald, please contact the Carroll County Cooperative Extension Service at (502) 732-7030.


Christin Herbst is the Carroll County Extension agent for agriculture and natural resources. Call her at (502) 732-7030 or send e-mail to Christin.Herbst@uky.edu.