You find yourself wondering how this kind of damage could have happened without your even being aware of it. And you’re obviously concerned about whether it could get a lot worse.
Folks, let me tell you that this is Minor League compared to a couple of other examples I’ve come across, some in my very own yard.
This is all the work of woodpeckers and sapsuckers. They peck away at trees, but they normally don’t do a great deal of damage. Sapsuckers open small wounds, then they’ll come back days later and feed on the sap that flows from the openings. Woodpeckers may be searching for surface insects on which to feed, but their holes really do not suggest that insects are present within the trees’ trunks.
In almost all cases, trees will quickly heal across this kind of “damage,” so I rarely recommend any kind of treatment. The birds are protected species, so you mustn’t do anything to harm them. Pretty much, my suggestion is just to move on to find something else to worry about. (Politicians assure us that there are plenty of other options available.)
In a few cases, however, damage can be so thorough and widespread that you realize you must do something. That was the case the day after I planted a new tree-form Nellie R. Stevens holly along our drive. The pileated woodpecker made it his all-day project to peck away at the new tree’s trunk. Once I saw what was happening, I scared him away and applied paper tree wrap from the ground up to the lowest branches to protect the wounds from insects and decay – and to discourage the bird. It worked, because my little tree has doubled in size and has been loaded with berries all winter.