Bark Beetle Population At All-Time High


Pine and the entire Rim country is experiencing an extreme level of bark beetle activity. This activity is being brought about due to the unnaturally dense conditions of the forest and severe droughty weather over the past six years.

Because of fire suppression activities over the past century and exclusion of timber cutting in recent decades, there are 10 to 20 times more trees per acre compared to pre-settlement conditions. Competition for resources such as space, sunlight, nutrients and moisture causes a tremendous level of stress on the trees.


Many of the trees in the lot north of the Rim Country Mall are infested with the bark beetle and are scheduled for removal.

Due to the winter drought of 2001, many pine trees this summer have moisture levels approaching zero, forcing the trees to shut down. This means the needles are not respiring and moisture and energy are not flowing through the cambium.

Populations of bark beetles also are at an all-time high. These populations are the result of an unlimited amount of food available in the form of overstressed pine trees due to extreme competition for resources. In addition, mild winter temperatures over the past several years have not affected over-wintering beetle populations.

The bark beetles in the regional Payson area are composed of six to eight native species in the genera of Ips and Dendroctonus that attack ponderosa pine. Ips generally attack the top portion of the tree in the early summer and Dendroctonus typically attack the lower portion of the tree in late summer into the fall (exceptions exist, but to provide a quick explanation, please let this suffice). Each is a very small insect, typically less than a quarter-inch in length. Fertile adult beetles bore into the inner bark (cambium layer) of a pine and lay eggs. The eggs hatch into larvae and proceed to eat the cambium, creating narrow galleries. The larvae proceed to feed until they pupate.

This year, officials expect bark beetle activity to continue until freezing temperatures set in. All tree size classes and densities are susceptible. Although the beetles tend to select stressed and unhealthy trees, populations are high enough to overwhelm even healthy and vigorous trees.

At this point of the infestation, there is little option left for the homeowner to control the situation. Infestation is evident by identifying pitch tubes (crystallizing sap where the beetle made its entry) and/or fras (reddish sawdust-like excrement of the beetle larvae) in the sap, bark or at the base of the tree. A tree that is fading to light green then to reddish brown is usually already dead. As trees are infested, it is recommended to have the trees immediately removed from the property. If slash and other portions of the cut tree remains on the property, it should be treated to prevent its availability as a food source as well as the emergence of beetles within the bark. Wrapping in plastic, chipping, peeling or debarking, or burying can be effective slash treatments. Place slash in full sun to speed the drying process.

Once a tree is infested, chemical treatments are not recommended. Systemic insecticides applied at the root system or injected have not been found to be effective.

Healthy trees with good vigor are most resistant to bark beetle activity. Fertilization is not recommended. For a homeowner to increase tree vigor, it is recommended that trees be thinned out to limit competition. One rule of thumb for thinning is "diameter plus seven." Desirable trees are selected and marked with colored tape. The diameter of the tree is measured at 4.5 feet above the ground. Convert these inches, for example, 15 inches, to feet and add 7. A radius of 22 feet around the tree should then be cleared of other pines, juniper and cypress. Native grasses and wildflowers can then be seeded to fill in the open areas.

Another important technique to increase vigor is selective watering. As it is probably not feasible to water every tree, the homeowner should select several trees within a reasonable distance of a water source. These trees should be watered using a soaker hose place just beneath the dripline (umbrella) of the trees. Watering selected trees at least once every six weeks throughout a winter drought is probably the most effective treatment a homeowner can do to maintain healthy, vigorous trees the next summer, thus helping their trees to be as resistant to bark beetle attacks as possible.

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