University of Illinois Extension

Tree Wound Dressing: Helpful or Hinderance?

Many gardeners have experienced that awful moment when the lawn mower or weed whacker accidentally comes in contact with the bark of a valued tree in the landscape and a wound is created, said a University of Illinois Extension Educator.

"No matter how careful you are, sometimes accidents happen and then you're left wondering, what you can do to help the tree repair this wound," Candice Miller explained. "The answer is really to let the tree repair the wound on its own in most cases."

Upon being wounded, trees begin a natural process of callusing over the wounded area with new bark and wood. In the spring when trees are growing vigorously, this process with naturally occur quickly. In other times of the year when growth is not as vigorous, try to keep wounded trees growing as vigorously as possible. Trees should be fertilized properly and watered during droughts for example.

"Keeping the tree as health and happy as possible is really your best bet," she said.

However, in the case of some trees, a wound made during the active growing season, may mean that insects or diseases could be more attracted to the wound and potentially pass on pathogens. Pruning wounds on oak and elms can attract borers and beetles that are carriers of diseases such as Dutch elm disease and oak wilt.

"In this case, some may recommend that a tree wound dressing be put on that wound," she explained. "The effectiveness of this is debated though. A tree wound dressing is a petroleum-based product used to cover freshly cut wood to inhibit decay or insect infestation. According to research done by Washington State University, wound dressings do not prevent entrance of decay organisms or stop rot from occurring. They do on the other hand, seal in moisture and decay, sometimes serve as a food source for pathogens, prevent wound wood from forming, inhibit compartmentalization, and eventually crack, exposing the tree to pathogens. All of which are a problem."

The research indicates that if you must prune a disease-prone species when insects or fungi are active (i.e. during the warmer times of the year), a light coating of an insecticide or fungicide may be warranted.

"Other than that, avoiding wounds is the best practice," Miller said. "Mulch around trees and shrubs to avoid mowers and weed whackers from coming close to trees, and prune during the dormant season when insects and pathogens are not active."