Preventing Winter Sunscald on Trees
By Ron Honig
Homeowners with young trees should consider protecting the trunks from a problem known as winter sunscald. Sunscald occurs during the winter months on trees when the sun warms up the dormant tissue on the south or southwest side of a tree’s trunk to the point that the bark’s tissue loses its dormancy and the cells become active. Then, when the sun sets and cold night temperatures return, the tissue on the sunny side of the tree can freeze and a strip of bark be killed. The damaged bark tissue becomes sunken and discolored in late spring. Damaged bark will eventually crack and slough off.
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. 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 recover from sunscald but need extra care, especially watering during dry weather, as a portion of the water transport system has been destroyed.
I have seen a few good examples of sunscald on trees in our district over the last few years. This fall and winter we are seeing large shifts in temperatures from mid-day to night, thus the 2021-2022 winter may present an opportunity for winter sunscald to occur.
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 heavy white-colored paper wrap. Homeowners can be creative in producing their own home-made protective wrap.
This 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 best 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.
Not all universities agree on the best way to avoid sunscald, but K-State’s horticulture department still recommends taking action to prevent sunscald on young, thin-barked trees.
