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I have a small/medium sized Ulmus parvifolia that has been doing quite well since we bought it several years ago. But, I just recently noticed (I admit I don't thoroughly examine my trees regularly - I don't know how old these holes are) some holes in the trunk. They are in 3 'groups' of 2, 3 and six holes, all about 4 1/2 ' above the ground and seem to mostly be in a horizontal arrangement. i can see NO other holes lower or higher up or on any branches.
I have read a little about Borers. I pulled a few pieces of the bark away looking for bugs hiding under the flaky bark. No luck. Just now however, I used a piece of stiff wire to probe the holes/kill grubs and discovered the holes are ALL only about 1/16-1/8" deep.
Does this help narrow-down what kind of creature created these holes?
I may try to treat with Bayer or Bonide 'merit' based systemic starting next march but, if I could somehow confirm this is minor damage and/or perhaps unrelated to any harmful bug infestation, I might ignore it.
You are welcome. I think the tree should be fine as is. The holes are shallow and it sounds like they barely broke through the cambium. Sounds like they were after bugs rather than sap or a hollow hole for nesting. We have a mated pair here that regularly check out the live oak and pines and the trees haven't exhibited any stress from it.
We hear and have often spotted woodpeckers in our area so, most of the data lines up best with that being the source of the holes. And it's exactly as you said, they seem too shallow to have been insect damage. These holes would offer zero protection from the elements for a grub. Perhaps a hungry woodpecker was just 'testing' the tree?
thanx again - I'm just going to monitor the tree I guess. It has done a good job of healing itself in a few places where I have trimmed/shaped it and these wounds are much smaller.