It was once thought that prune salve protected trees from pruning wound infection. However, horticulturists now know that prune salve may actually prevent trees from protecting from healing themselves and some prune salves actually serve as food for certain micro-organisms. But while you should avoid using prune salve on healthy trees, weak trees and those suffering from insect, bacterial or viral infections can benefit from prune salve. If properly applied, prune salve can give the wound essential protection from the spread of infection and prevent excessive sap bleeding which can further weaken compromised trees.
Prune large (greater than 2 inches in diameter) branches. Prune branches smaller than 3 inches all the way to their base with a pair of sharp, disinfected pruning shears. Branches larger than 3 inches in diameter must first be sawed one foot away from the trunk by cutting 1/3 of the way up from the bottom of the branch and then all the way through the branch from the top down. Then saw the remainder of the stub off from the top so that the wound is flush with the trunk.
Allow the pruning wound to dry.
Apply the prune salve according to the manufacturer's instructions.
Monitor the pruning salve coating once a month or so for the first year that it is on the tree. If it becomes cracked, re-apply the coating.