By pruning at this time of year ... had a chance to finish all of that work and acclimate to the cold. Both trees and summer-blooming shrubs should be pruned in late winter to early spring ...
Initial pruning and training of young trees is best carried out in spring, just as the buds are breaking. Other pruning to correct problems and encourage fruiting should be carried out in summer – ...
Note: Do not prune more than 20% of your tree in a single year. This could put it into shock. If you over prune, your tree will dedicate its energy to growing new leaves instead of fruit.