Here’s a link to a great article put out by the Penn State College of Agricultural Sciences. It describes how fall pruning can adversely affect trees and vines. Whether I knew it or not, I was always a suspect of pruning in the late fall. I always wait until spring and prune my vines and trees at bud swell… just before bud break. My reasoning is that appendages sticking out into the cold air are the first to get frostbite, and die.

An analogy would be just like how the tips of your fingers or toes get cold first when you go outside in the cold weather. If you didn’t do anything about it, you would suffer frostbite, and in the extreme, tissue death. If you didn’t have any fingers, what would be the next thing to freeze? Your knuckles? Your hand? I always leave pruning for the spring, when things are firing back up. It’s also more obvious as to what wood is dead and needs to be removed before the growing season. One thing for sure is, during the course of a cold winter, there will be a lot of frozen limbs and vines that die from frostbite.  So, I wait to prune my fruit trees and vineyard in the spring.

Here’s an abstract of the article

It seems that we are experiencing more unusually warm periods during mid- and late-winter, so trees may be more susceptible than in the past to moderately low winter temperatures. Lessons from years in which there was a sudden drop in temperature indicate that trees most injured were those that lacked adequate vigor, those that were too vigorous, and those that had been pruned before the cold event.

Read the full article here