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Sunday, October 14, 2018

Repairing Plum Tree from Borer Damage

Q. I have a ‘Green Gage’ plum tree that is 18 years old and produces plenty of plums each year. In August I saw sap coming out of one branch and along the trunk in several places.  Last week the bark started to separate and it looks like the trunk is starting to split. The leaves on that limb are starting to die. This side of the tree receives the west sun. All the other branches on the tree appear to be fine.

A. Green Gauge is a good plum for our desert climate and 18 is not old for a plum tree. Plums can be “sappy” compared to other fruit trees but from your description it sure sounds like borers. You won’t hurt anything, but I would take a very sharp knife that has been sanitized and start actively looking for borers.
            It is possible to remove the outer layer of bark covering the trunk and limbs and reveal the immature form of this insect, called the larva, causing the damage. Once exposed like this, it will die.
            Expose all the damage caused by borers down to healthy wood. Leave this exposed area open for healing.  I would say that about 80% of the time this is an effective way to remove the borer and allow the limb to recover.

What I Would Do

I would first remove some bark on top of the area where I think borers might be residing. Hold the sharp knife nearly flat and push the blade away from you to remove the bark. After removal, inspect the wood to see if it is alive or dead. If it is alive, stop and don't do anything more. If it is dead, remove all of this dead bark until you see bark that is alive. If you find evidence of borers, try to find them in this dead area and remove them. If the borer damage is extensive it might require removal of the limb or branch. Do not paint this area but let it heal in the open air.
Using a sharp, sanitized knife to remove the bark that surrounds a borer infested limb.

Removal of the dead wood caused by borers
Successful removal of borers the previous year and the tree showing signs of healing.

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