Wild West District Article
By Ron Honig
December 20, 2023
Preventing Winter Sunscald on Trees
Southwest Kansas is known for its mild winters and as we begin the first days
of winter, we see the familiar fluxation of temperatures between the low sixties and the freezing mark. These types of ranges, while usually less abrupt as we move deeper into winter, can lead to an ugly injury to young trees known as winter sunscald. Homeowners or small orchard owners should consider protecting the trunks of their young or thin-barked trees from this common problem.
Winter sunscald occurs during the winter months on trees when the sun warms up the dormant bark tissue on the south or southwest side of a tree’s trunk to the point that the bark’s tissue loses its winter dormancy and the tissue cells become active. Then, when the sun sets and cold night temperatures return, the tissue on the sunny side of the tree freezes and a strip of bark is injured or killed. Research done in Georgia on peach trees has shown that the southwest side of the trunk can be 40 degrees warmer than the shaded bark.
The damaged bark tissue becomes sunken and discolored in late spring. Damaged bark will eventually crack and slough off leaving exposed inner wood and a trough appearance recessed into the trunk.
Trees most susceptible to sunscald include thin-barked species such as honeylocust, fruit trees, ash, oaks, maples, lindens and willows. Young trees are at greatest risk.
Trees often survive sunscald but need extra care, especially watering during dry weather, as a portion of the water transport system has been permanently destroyed.
I have seen a number of examples of winter sunscald on trees in our district over the last few years. Horticulture experts believe the greatest danger for sunscald occurs in late winter as we see a mix of warmer daytime temperatures among cold nights.
Prevention usually involves wrapping young or recently-planted trees with a light-colored tree wrap from the ground to the start of the first branches. Commercially produced wraps are available from garden stores in the form of a flexible heavy plastic strip that is coiled around the trunk or a heavy, white-colored paper wrap. Homeowners can be creative in producing their own home-made protective wrap. It is important that the wrap be light-colored to reflect sunlight and keep the bark cool. The use of a dark-colored wrap may only worsen the potential for a problem.
This wrapping process is best started in November and removed the following March, but if you have susceptible trees, wrapping them anytime may be better than leaving their trunks bare all winter.
Commercial orchards will sometimes use light-colored paint as a substitute for tree wrap. Paint may not be the most aesthetic choice for protecting young trees in the landscape, but if you wish to make a whitewash solution for an orchard, dilute white, interior latex (not acrylic) paint with an equal amount of water and apply to the south and southwest side of the tree trunks.
Sometimes in Kansas, but more likely in southern states, summer sunscald can be found. This is a similar bark injury to winter sunscald however it is caused by direct sunlight causing heating of the plant tissue high enough to damage bark on a thin-barked tree.
Not all universities agree on the best way to avoid winter sunscald, but K-State’s horticulture department still recommends taking action to prevent winter sunscald on young, susceptible trees.
