dieback definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a disease of vascular plants characterized by a dying backward from the tip of twigs and branches and caused by parasites, insufficient moisture, etc.
dieback definition by American Heritage Dictionary
The gradual dying of plant shoots, starting at the tips, as a result of various diseases or climatic conditions.