By James Feucht, Ph.D., Colorado State University Cooperative Extension specialist, landscape plants.
A healthy tree has the capacity to chemically defend itself.
That's because trees have built-in antiseptics. When microbes and insects attack healthy trees, or when trees are damaged by lawnmowers, poor pruning practices or storms, compounds go to work in the vicinity of the wound to help defend the tree against infection.
Dr. Alex Shigo, a forest pathologist, has found that, when wounding occurs, a deciduous tree isolates the injury by forming phenolic compounds. Conifers form terpenes. These compounds manifest themselves as more-or-less wedge-shaped areas of wood adjacent to the wound. These areas "wall off" the injury slowing down or stopping invasions of microbes and insects.
Trees in poor health have a poorer ability to defend themselves because they have less reserve energy to form defensive chemicals.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010