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Williams: Thin-barked trees susceptible to bark-splitting condition

Posted: July 16, 2017 - 1:22am

I have received several calls about split bark, or vertical cracks along the trunk of young trees. This condition most commonly occurs on thin-barked trees such as dogwood, elm, maple, plum and cherry. These cracks can become long-term open wounds that are susceptible to insects, diseases and wood decay. Unfortunately, after this damage has occurred, there is no help we can provide the tree. Prevention is the best solutions and can be done with a little planning before planting.

Thin-barked trees planted in hot sites with full sun exposure in the afternoon are highly susceptible to a disorder known as sunscald. Sunscald can occur when the cambium cells - active, growing tissues under the bark - heat up too rapidly during sunny fall or winter days. Extremely cold temperatures following warm periods can also kill cambium cells in the trunk. Research has shown that the south side of a tree can be as much as 77 degrees warmer on a cold winter day than the north side of the tree. The newly activated cells lose some of their cold-hardiness and are injured when temperatures drop below freezing during the nighttime hours. The portions of trunks and branches facing south and southwest warm the most because they get the most direct sun and because they get sun later in the day when air temperatures are warmest.

Damage from sunscald injury can result in discolored bark, bark cracking, sunken areas from lack of growth, or sloughing of surface bark to reveal dead tissue within the damaged area. This damage will appear on the trunk's southern or western side. Damage from sunscald injury may eventually heal, but the damaged areas should not be painted or filled with any sealing substance such as paint or tar. Bark injuries from sunscald will reduce the tree's ability to take up water and nutrients at the roots and transport it to the shoots. Bark injuries from lawn mowers and string trimmers have the same effect. Newly planted trees, in the spring and summer, are often more susceptible to sunscald because they haven't had a chance to acclimate to their new environment. Trees planted too close to parking lots or driveways can suffer from sunscald as a result of the sunlight radiating off the pavement.

Sun scald can be prevented by applying commercial tree wrap or plastic tree guards to protect thin-barked trees for the first couple of years after planting. The wrap will reflect the sun and keep the bark at a more constant temperature. To wrap the tree, start at the base of the tree trunk and wrap up to the lowermost branches, overlapping each layer by a half-inch. Install the wrap on newly planted trees in the fall and remove the wrap in the spring after the last frost. Tree wraps are temporary and should not be used once the tree develops thick, corky bark. Newly planted trees should be wrapped for at least two winters and thin-barked species up to five winters.

keep in mind drought-stressed trees tend to be more susceptible to sunscald injury. Make sure trees are properly water during the growing month and increase watering amounts if drought conditions occur. Trees benefit from deeper and less frequent watering events. A layer of mulch around the base of the tree will help conserve soil moisture and moderate temperature. 3 to 4 inches of mulch will be sufficient.

Always avoid purchasing trees with bark injuries. Trees with these types of wounds may eventually recover but may be permanently stunted or short-lived. In more severe situations, bark splitting can girdle the tree stem and shut off the flow of water. These trees die suddenly.

 

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