How do tree wounds occur? Wounds can result from severe flush pruning cuts that damage or remove the branch collar around where a limb joins the tree trunk. Broken branches frequently are caused by high winds and the accumulation of heavy snow. Even an out of control weed-whacker can cause a serious tree wound.
Whatever the cause, it is important for the home gardener/landscaper to know the best course of action in dealing with a tree wound.
The answer is easy — do not apply a wound dressing! Wound dressings do not prevent the entrance of decay causing organisms and do not stop rot. However, they can do a lot of additional damage to an already stressed tree.
Dr. Linda Chalker-Scott, a horticulturalist at Washington State University, says there is not “one shred of scientific evidence” to substantiate the alleged wound healing properties of commercial products containing aloe gel, collagen, hydrogel or pectin.
Trees do not “heal.” Trees isolate damage through the formation of a “corky” material that both physically and chemically repels invasion. A callus develops at the edge of the wound and expands toward the center of the wound. The “corky” wound wood remains for the life of the tree.
Wound dressings create additional problems by sealing in moisture and decay, interfering with the formation of the “corky” wound wood and inhibiting the compartmentalization that helps to protect the tree. When it comes to tree wounds, allowing the tree to respond naturally is definitely the right answer!
The following information is provided by Chalker-Scott:
Like all living organisms, plants have natural resistance mechanisms to fight insect attack or disease.
• Covering wounds with traditional sealants inhibits oxidative processes, which in turn will reduce callus formation and subsequent compartmentalization.
• Optimal pruning time for insect- or disease-prone species is in the fall or winter when temperatures and infection rates are lower.
• 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.
• Sterilize pruning tools. Such measures can help reduce the transmission of certain plant diseases to healthy plants.
• Control disease spread through preventative management practices such as disposal of contaminated organic material and use of disease-free compost and mulch.
Because tree wounds can result from improper pruning, expand your knowledge of landscape or orchard tree pruning by reading the educational bulletins listed below. Both are free and available online.
“Training and Pruning Your Home Orchard” by Jeff Olson, PNW 400 Revised 2011, Oregon State University, University of Idaho, Washington State University; and “Pruning Landscape Trees” by Ray Maleike, EB 1619, Washington State University.
Judy English is a Washington State University-certified, Clallam County Master Gardener.
“The Myth of Wound Dressings” Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University (website: www.theinformedgardener.com).