Bark beetles are part of a natural forest and they generally prey upon weak trees. So anything that will weaken tree defenses will make stands more susceptible. These factors include, but are not limited to: drought, fire damage to roots or aboveground parts, lightning damage, construction injury, slash, or windthrown trees in vicinity, mistletoe infection, a concentration of livestock urine in the soil, or defoliation by insects. Another factor is that the host tree needs to be of sufficient size to be a suitable host for bark beetles. With ponderosa pine, the diameter of the tree must be at least 4 inches in order for viable offspring to develop in the tree and emerge to attack another tree. With other species of trees, the diameter of the wood may be larger or smaller to be of suitable host material.
Jeff Schalau, Associate Agent, University of Arizona, and Tom DeGomez, Area Agent and Regional Specialist, University of Arizona
