Loss of Bark on Ornamental Plum Due To Borers

Q. I have a flowering plum
which I first noticed this morning has a problem with loss of bark on the west
side of the trunk. My yard faces south. What should I do?

A. This is borer damage to the trunk. You can read more
about this insect and the type of damage it does to ornamental and fruit trees
and how to correct it from the links below.

Your picture was extremely helpful but the other thing that keyed be in was that you said it was on the west side of the trunk. This is the side of the trunk getting very hot in the late afternoon. Heating up on this side from the sun leads to sun damage. Sun damage to the trunk attracts boring insects. They like to lay their eggs on these kinds of damaged sites.

Since
you are not eating the fruit of this tree you can apply a liquid soil drench
insecticide. This product comes in several trade names so I cannot list them
all but the key chemical ingredient is Imidacloprid. This will be listed in the
active ingredients.

Homeowner version found in many nurseries and garden centers

Follow
the label directions and apply it after it finishes blooming.  Otherwise take a clean knife and clean up the
damaged area and let it heal as explained in the posts on my blog below.

http://xtremehorticulture.blogspot.com/2015/08/identifying-their-damage-and.html

http://xtremehorticulture.blogspot.com/2014/02/mechanical-control-of-borers-in-fruit.html