Question
Our maple tree which is approx. 20-30 yrs. old is losing limbs from the bottom up. We have lived here for almost 10 years and the tree has always been healthy. This is the first season that we have had any problem with it. There is a vertical crack in the bark that runs from the ground to about 8' high. The crack is dark and moist looking. There is no other obvious problem with the tree. Could the crack be the culprit and what can we do to stop the damage?
Thank You for your time
Tom Wilson

Answer
Lower limbs self shed from being shaded as the tree grows older. The cracks sound like sunscald.

Sunscald is another form of winter injury that can cause cracks and splits. Sunscald occurs when cells in the living tissue beneath the bark thaw out on sunny days. This occurs mainly on the south or west side of trunks and branches. These cells rupture when they re-freeze at night. The tree is injured when enough cells in a given area rupture. You'll notice the injury the following spring as a discolored, sunken area. Fungus infections often invade trees via sunscald injuries. Young, thin-barked trees are most susceptible to sunscald injury. These include maple, honey locust, linden, and mountain ash. Heavy pruning on neglected trees exposes sections of bark that have been protected from the sun's direct rays for years, predisposing them to sunscald injury.



I would spray the area with an insecticide called Merit to prevent borers from entering the trunk. And fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Apply the fertilizer just before a rain storm and you will not need to water.  This will increase the health of the tree and allow the tree to better stave off any insect or fungi.
In general I would not be too concerned about the crack except for borer prevention.