My apple trees appear to have something boring into them. Tree in the attached picture is right next to cherry trees, and the cherry trees don't seem to be affected, only apple trees. Can anyone tell me what might be causing this and how to stop it?
The holes shown in the first photo are made by Yellow-bellied Sapsuckers which are known for their precise tree damage. In search of sugary sap, the bird often chooses maple and apple trees but they’ll go after lots of other tree species, too. They feed on sap inside the tree and the insects that are drawn to it, like beetles and ants. Woodpeckers mainly eat the insects, not sap. Sapsuckers peck perfectly neat horizontal (or sometimes vertical) rows in tree bark. Although there is no way to repair woodpecker damage, you can deter them by wrapping the affected areas in burlap or small gap chicken wire. From: What Causes Tiny Rows of Holes in Tree Trunk (Maple, Oak, Apple)? | Davey Blog
The sapsuckers of course have nothing to do with the old wounds you show in your second, third and fourth pictures.
The apple tree looks quite old. It could be that the side trunk and branches were diseased and/or rotting before they were sawn off but has continued nonetheless. It looks as though the cuts were not as close to the base of the limbs as they should have been and that could also have led to rotting you see now. I'd be getting out the chainsaw and looking for one or more new varieties of apple to replace that old one.
California Cooperative Extension has lots of information about fruit growing, try asking about your trunk damage at your nearest branch office.
