Answer: Unfortunately this does not sound good. The ornamental cherries are sometimes considered to be short lived trees in the landscape due to their many potential pest and disease problems. There are many possible causes for internal damage ranging from ice storms to poor formative pruning to disease or pest problem, but that split indicates a serious problem with the main branch that potentially makes it unsound and liable to break off. The white powdery substance on the bark could also be a sign of an infection such as canker. You will need a specific diagnosis of the problem(s) before you can decide how to proceed and whether or not the tree can be saved. It is very difficult to diagnose these kinds of symptoms long distance, so I would strongly suggest you consult with your county extension and/or a professionally trained and certified arborist with experience in ornamental trees. I'm sorry about your tree.
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