Winter kill on apples - followup
So with it approaching the 4th of July, I think it's time for me to reassess my winter kill question. For those that may not have seen or remember my original post on this: I had planted about 24 bare root apple & pear trees last spring, plus a few cherries, a plum and a few nut trees. Most grew well showing good shoot growth during the year. However late winter early spring I noticed that many of the branches of these trees had become shrunken/shriveled a bit, and slightly darker colored. I had painted the main trunks/branches white (50/50 latex), so there was not much more to do but wait and see.
Now that its safe to assume that anything that is going to grow has, I have taken a count of what finally happened.
All of the trees lived. And most of the ones which had shrunken branches recovered. The branches swelled and leafed out. So my concern was mostly unfounded. A few of the new growth tips died back an inch or so, but generally most or all of last years growth survived and is growing this year. (I should mention that all this concern was with the new trees. The few older apples here did not show the branch shriveling, although there was some darkening of the bark over the winter)
However five of the new trees (about 17%) did not recover. The shriveled branches did not plump up again, and no growth ever started from those shriveled parts of the branches. Further down on the tree, the branches/trunk were not shriveled, and new growth did start from these locations this spring. Often times from the branch attachment point to the main trunk. If one looks carefully one can see a clear point along the branch where the change happens, it is full and round on one side vs shriveled on the other.
I would like to understand what caused these 5 trees to not recover on these branches. There does not seem to be any pattern to which branches survived or not. Painted or not, new growth vs old, there was no conclusive pattern here. This past winter was a mild one by our standards. Min temps of -10F, good snow cover almost all winter. Very sunny and windy (as usual for us). We did have a bout of warm weather early on like most of the country, but the trees in question never leafed out from these branches, either in the early spring or the real one later.
Any thoughts as to what might have caused this? Winter kill? Moisture stress? Sunscald (I did not paint until Dec/Jan)? And what, if anything might I do to avoid this in the future?