Late fall and early winter isn't the ideal time to trim a tree, but there are certain issues that need to be tended to before winter weather arrives. Otherwise, there is an increased chance of damage when the problem branches are weighed down by snow or tossed around by winter winds.
1. Stubs and Nubs
Stubs and nubs left behind by broken branches should be trimmed down before winter arrives. The reason is exposure. A tree can't properly heal over a branch stub, so the wood tends to decay on the trunk. This can provide an entrance for a variety of wood-boring pests and disease organisms. Stubs and nubs should be cut back to the branch collar that sits flush to the trunk. The sooner the branch breaks off, the better.
2. Dead Tips
The tips of branches will sometimes die back. This is even more likely to have occurred in areas that have suffered a drought. The dead, dry tips aren't just unattractive, they will snap off in winter winds. If your tree has suffered some tip dieback, trim the branches back to the nearest bud on still-living wood. Completely dead branches should be removed at the base.
3. Crotch Complaints
The tree crotch is the angle formed where the branch joins to the trunk. An overly narrow crotch, where the branch grows nearly vertical, is a problem because the vertical branch may result in a split trunk. Even more problematic in winter is the overly large crotch, which causes the branch to droop downward. These branches will often break off when weighed down with snow. Trimming off branches with overly narrow or wide crotches is advised.
4. Too Much Friction
Branches shouldn't be growing so close that they rub against each other. The friction will wear through the bark and make at least one of the branches more prone to diseases and dieback. There's no need to fully thin out the tree crown before winter, but any larger branches that rub should be trimmed out so that friction from winter wind doesn't lead to issues.
5. Ugly Cankers
Cankers are swollen or sunken wounds on tree branches. They are sometimes caused by insects, but often fungal or bacterial pathogens are the cause. If there are any branches with visible cankers prune them out before winter. This may prevent the issue from spreading to healthy wood.
Contact a tree trimming service for more information regarding this process.