Answer: I would suspect the drought may have caused the die back, with weakened branches being even more susceptible than usual to drying out over the winter as well. However, there are also numerous pests and diseases that can cause this so if the problems continue you might want to consult with your county extension as to additional possible causes. In the meantime, prune out anything that is dead and remove and destroy the trimmings and any dropped foliage. Start at the top and work your way down until you find live wood. When removing just a portion of a branch, try to cut just above a smaller branch that is directed in the way you would like the subsequent growth to go. If there is no live branch, cut as close to the base as you can.
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