Pruning a Crabapple Sergent Tree
Pruning is an extensive subject beyond the scope of what can be explained here. I can give you some resources and basic tips.
Prune when the tree is dormant in late winter or early spring. On crabapples this will cause the loss of some flowers. So, you may want to wait until after flowering and then prune.
Any dead, diseased or damaged branches can be pruned back to a healthy branch union or to the trunk. See the attached articles for correct pruning techniques, being careful not to cut to flush with the trunk or leaving too long of a stump which opens the tree to rot.. Any branches growing inward can be pruned. For crossing branches that rub against each other or grow too closely together select one branch and prune the other off. . Never reduce the crown total by more than 1/3 per season.
You may want a trained professional, a certified arborist, to come out and prune this plant for you. To find these professionals who have training in woody plants, care, diseases and pests, search by ZIP Code- www.treesaregood.org