I'm not sure if this is a fungal issue, but it's my best guess. I have a few apple trees that have sections of the bark on the trunk, mostly just below the first scaffolds, that are blackening and becoming hollow under the bark. The bark easily chips off and the cambium layer is gone. Some show healing callus around the edges, but others appear more jagged on the edge. I'm guessing it's fungal or moisture related because mostly it is on the north/northeast side of the trunks and the trees that have it the worst are somewhat shaded by a tall row of Japanese fantail willows. (The willows are a long story for another time and place.) Nearly all these trees have damage from yellow-bellied sapsuckers. Apple varieties vary - Winekist, GoldRush, Wolf River. So, is it a shading issue? Do the willows have some allelopathic effect? Do sapsuckers come before or after the problem? Any thoughts would be much appreciated.

I have seen this too, and would like to hear what people think.

I've been doing a little research and what I'm seeing in our orchard sounds like Black Rot (Botryosphaeria obtusa), aka blossom end rot or frogeye leaf spot depending on its development stages. Looks like it is time for me start gathering fresh manure and local clay!! Can anyone help confirm this?

Here's a theory. We're all familair with "southwest injury" being splits in the bark (going as far as cracks in the wood) resulting when dark tree trunks thaw in the winter sun only to freeze too quickly when the sun goes down in the southwest. Thus the advice to whitewash the bottom few feet on that side of the trunk to reflect the solar heat and so forth. This cold injury isn't always as obvious as split bark... sometimes resulting in deadened cambium tissue instead... which you might notice as darker, sunken spots. Snow cover reflects light to the north side of the tree as well, and given the right kind of day, can thaw that side as well. And the spot this usually occurs is on the underneath side of scaffold branches. It's in these "tree armpits" functioning as solar collectors where the damage occurs. This often is not noticed for a year or two or three until the bark falls off. Opportunistic fungi like black rot move in during this time. The callus dynamic is the tree attempting to zone off the damaged area but I can't say why you see it on some trees and not on others. I will let someone else speak to sapsucker pyschology!

Yellow-bellied Sapsuckers are the culprit if the holes are in line and uniform. The damage they do comes prior to any infection. Since they are drinking the sap that oozes from the wound, they will actually avoid an unhealthy area looking instead for clean and free running sap. This is why they make a new row for each feeding. They and other woodpeckers looking for the meat course to their meal (ie insects) will head for diseased or dead areas where insects are likely present. These areas will likely be more of an excavation. I believe most woodpecker species are protected, so I am not sure what you can do to shrink their numbers.

I found a link to the site at Kerneysville. I have experienced a little of all the examples. Sanitation and pruning seems to be the key for our orchard in the humid Midwest. http://www.caf.wvu.edu/kearneysville/disease_descriptions/omblackr.html