Holes in the trunk of apple tree
Thank you for the question. If picture enlargement is accurate, it looks like there are multiple holes in rows in many other places on the tree as well as in the section you photographed. These holes may be caused by yellow bellied sapsuckers, a bird in the woodpecker family. This bird drills many evenly spaced holes in an effort to get at the sap. It also ingests the insects that are attracted to the sap. This damage isn't usually serious but if there are lots of holes that go all the way around the tree, decline or death of the tree can result from this girdling. Insects attracted to the sap can also cause problems. Read more here and learn ways to protect the tree: http://www.clemson.edu/extension/hgic/tyk/2008/tyk01.html
Here's another link showing holes similar to yours: https://agrilife.org/etg/2012/03/20/sap-sucking-sapsucker/
If the tree hasn't been doing well in the last year or so, you might want to have a certified arborist come out and evaluate its health. Here's a link on how to locate such a professional: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/how-to-hire-a-professional-arborist/
Thank you for contacting Extension.