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Sometimes trees develop wounds called "cankers". These are horizontal cracks in the bark. They slowly expand until they have encircled the tree, cutting all of the "tubes" that carry nutrients from the roots to the branches, killing the tree. I have always been told that there is no known cure. However, years ago I stopped a canker that had progressed one third of the way around the trunk of a birch tree in my yard. That tree thrived for the next 30 years.
The "miracle" substance I used was triple antibiotic ointment (Neosporin), which is available at every health and beauty aids department in the country. Simply reach under the edge of the bark with any kind of narrow tool, and scrape out most of the rotten wood, bugs, and debris. Then insert the nozzle of the Neosporin tube under the bark and proceed from one end of the canker to the other, squeezing the tube until the ointment begins to squish out from under the bark. (Do this on top and bottom of the canker).