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Sunscald is a fairly common physiological problem found most commonly on young, thin-barked
ornamental and fruit trees. There are two subcategories of sunscald based on season
(winter and summer), and both are inherently caused by the same factor; death of
bark tissues caused by high temperatures.
Winter sunscald or frost cracking, which is less common in Arkansas, begins in the
Death of cells in the bark is caused by rapid fluctuations in temperature. Research
suggests that during the winter, frozen tissue on the south or southwest side of the
trunk which is also being heated by the sun, thaws and then rapidly refreezes. These
rapid fluctuations in temperature are most likely to occur near sunset or during the
day as clouds pass blocking the sun exposure on the trunk. Research at the University
of Minnesota suggests that this tissue death is also related to moisture stress.
Summer sunscald (Fig. 1) is likely the more common type in Arkansas and is related to death of bark tissue
as a result of lethal temperatures from sun exposure. Summer sunscald would rarely
be encountered in undisturbed forests except for young trees on the edge.
Summer sunscald is more common on fruit and ornamental trees such as maples (Acer; sugar, red, hybrids), sweetgum (Liquidambar), linden (Tilia), ash (Fraxinus), honeylocust (Gleditsia), Eastern white pine (Pinus strobus), and apple (Malus). The problem is common on the lower section of young trunks and the south or southwest
The initial death of trunk tissue is rarely seen. Early symptoms may be difficult
to interpret as it will consist of discolored bark (similar to a canker) and some
small vertical cracking in the bark (Fig. 2).
In the spring there may also be ‘bleeding’ from the damaged area. As time progresses
bark will begin to slough off. Late stage sunscald is easier to identify as the classic
vertical fissure down to the interior wood (xylem) will be visible (Fig. 2). Margins
of the vertical fissure may show healthy wound closure which will be further pushing
dead bark off the tree. Loose pieces of bark can be removed but avoid cutting or tearing
into healthy tissue.
Pruning paints should not be applied to the wound area. It is not uncommon to see a variety of insects in the wound fissure but these should
not be of great concern. Very large sunscald wounds can contribute to tree death
and is a likely area for future failure of the trunk (i.e. trunk breaks in this region).
Understanding the underlying cause (i.e. lethal temperatures) of summer sunscald helps
understand the typical treatments. The most common management strategy is to cover
the lower trunk with light colored materials.
A number of options are commercially available including rigid corrugated plastic
tree guards, kraft paper tree warp, and breathable white fabric tree wrap (Fig. 3).
Do not use black or dark colored tree wraps (Fig. 4) since they intensify the temperature problem. Proper installation should ensure that materials do not girdle the trunk as the trunk
Trunk shading materials will need to be left in place for several years until the
trunk achieves enough thick, textured bark to buffer the extreme temperatures or the
canopy is wide enough to provide natural shade for the trunk.
While some of the wraps may result in elevated moisture or provide a hiding place
for insects, research has not demonstrated these issues to result in increased problems
for the tree. Besides wraps and guards/tubes, some suggest painting the lower trunk
with white latex paint to reflect sunlight. Make sure the paint is not toxic to the
plant tissue. Although it has been suggested that trees under water stress are more
prone to sunscald this has never been confirmed by research. Watering during prolonged
periods of drought would still be recommended to reduce the overall stress on trees.