Protecting Pruning Wounds
Applying an asphalt emulsion or other materials to pruning wounds to protect them is of doubtful value. The purpose of these emulsions is to protect the cut surface from wood-rotting organisms and to prevent checking as the wood dries. When exposed to the sun, however, the coating often cracks. Moisture from rain, sprinklers or dew can then enter the cracks and accumulate in pockets between the wood and the wound covering. That moisture makes the wound even more susceptible to wood-rotting organisms than one with no wound cover application.
In some situations, for aesthetic reasons or for maximum protection, the practice may be justified. Allow the wound to dry before applying the coating to improve chances for good bonding. Examine the coating several times the first year and retreat if the coating has cracked.
This article was prepared by students and professors at Michigan State University Extension, Home Horticulture.