I have several mature crabapplees that I have trimmed approximately every three years to maintain their shape. I know the best time to trim them is late winter or early spring but last year with the ice storms I worried about many of the branches that were weighed down with ice so I was thinking of having them trimmed right before Thanksgiving. Would this harm the trees or make them more susceptible to disease come spring? Thank you for offering this service.
Late winter to early spring is a better time based on wound exposure. Pruning in fall leaves wounds exposed through winter. Pruning closer to spring means a shorter time before wound closure begins. You can prune in late fall and many trees like maples and birch that bleed are done at that time. It likely would not harm your trees but why take a chance. Since most ice storms come in late winter you could schedule pruning later in February much like what is done for apples in orchards.