They are very likely the exit holes made by the adult round headed apple borer. The larva have been in your tree a year or two. initially eating cambium near ground level and then moving down into roots, the adult beetle has now chewed up and out. The damage from that round is done.

Inspect the tree and any other apples from soil level up about 2 feet, with greatest attention to the first 10". You want to look for any frass(wood dust), sunken bark, or oozy weeping(especially aer prolonged rain). These are indicators of the next generation of larva eating at the tree....cut open to outer bark and you will find brown or yellowing voids....follow thes until you find the larva, they may be small. So long as your chasing the damaged areas don't worry about how much bark your cutting away, try not excavate into live healthy green cambium. If you find one there are likely to be more.

Check again in about a month. White paint on the bark reportedly deters the adult beetles from egg laying....I don't buy that, but it does make it much easier to see the early signs of larva and get them before they do too much damage.....which can be extensive on young trees. Older trees with thick bark have less of a problem.

Rob,

You have solved a mystery I have had for a few years now. One of the trees on the property I inherited a few years ago had an apple tree that we actually just pulled down. It was at least 30 years old and came down with just a few of us pulling on it. When it broke off there was most HIDEOUS white grub I have ever seen. Truly huge and hideous. For some reason I could not find any information on it at the time. It (or they) did kill the tree.

We had quite a problem with them for a spell. Almost made me jump ship on organic and apply lorsban. But with steady work the last two years have been better....it's amazing how much damage a young tree on a vigorous rootstock can bounce back from.....if you get the grubs before they drop down below soil line.
My understanding is Generally the adults won't travel too far, so once present you need to really watch the surrounding trees.
Supposedly keeping grass and weeds cut back around trunk deters them some as they are less sheltered and hidden while laying.....don't know if true.

White paint and steady THOROUGH summer inspections have worked best for us. But I can't imagine doing that on anything more than a couple dozen trees.

Thanks for the response and sorry for my slow same.

I will inspect the other trees, there are only four.

When we had peach trees downstate, we sprayed with horticultural oil in the spring to prevent borers. Will that help prevent anything here?

Thanks again,

G

I'm losing a cherry tree this year to what I suspect are flatheaded apple borers, or something just as ugly. The wounds go several feet up the trunk. OBviously I need to look out for my other trees. When is the best time to apply the paint for protection?

Thanks for the response and sorry for my slow same.

I will inspect the other trees, there are only four.

When we had peach trees downstate, we sprayed with horticultural oil in the spring to prevent borers. Will that help prevent anything here?

Thanks again,

G