Article by Shawn Kelly, Forestry Assistance Program Forester for the Allegan, Barry, and Ottawa Conservation Districts
Under some conditions rapid expansion of the living inner bark can form a vertical crack in the bark, or a “split.” This is especially common on young smooth barked species such as maple and beech. If you look closely at a new split and you are able to see the wood below, this is likely a “frost crack” or the result of sunscald.
Sunscald most often occurs on the southwest side of young trees with thin bark. On a warm winter day direct sun can heat exposed bark substantially. If this heating is closely followed by freezing temperatures, often at night, death of the inner bark may occur. The injury will not likely be visible until spring growth resumes, and then appears as sunken or discolored bark. The bark may then split or fall off in patches or vertical strips. Often spitting is accompanied by sap “bleeding”. This is a common phenomenon and is a result of high sap pressure within the tree associated with this time of year (think maple sugar). Wrapping the trunks of young trees with a commercial tree wrap made of insulating paper in November can prevent sunscald. Trunk wraps must be removed by early spring.
Frost cracks are caused by conditions similar to those responsible for sunscald. In late winter and early spring, water in the inner bark and in the wood expands and contracts under fluctuating temperatures. Rapid expansion and contraction of water within the wood and bark, particularly under freezing night temperatures, can result in a crack. Recent evidence suggests frost cracks develop as a result of a previous trunk injury. Frost cracks may be up to several feet long and are often found on the southwest side of the tree. Rapid expansion of the inner bark can also occur as a result of other fluctuating growth conditions. Dry weather followed by wet weather can result in sudden growth that may cause splits. Avoiding fertilization late in the growing season can reduce the incidence of splits. Instead, wait to apply fertilizer until after the leaves have dropped in the fall.
Splits and sunscald are usually not fatal although they may allow the entry of insects or disease. The tree will normally heal by itself through growth of the living inner bark on the sides of the split. Research has shown that commercially available wound paints are not helpful to this healing process, and so are not recommended for treatment of splits or sunscald. Tracing around the wound with a sharp knife to remove loose bark may stimulate growth of the cambium and speed healing. Ensure the knife is sterilized before use, and carefully remove no more than ½ inch of bark from around the wound. Applying fertilizer in the spring may also help the healing process.
You can contact the Allegan, Barry, and Ottawa Conservation District Forester, Shawn Kelly, for more information regarding this and other forest health issues by emailing firstname.lastname@example.org or calling (269) 948-8056, ext. 114.