QUESTION: I have several Arizona cypress trees which are dying. There are holes in the trunks and the tips are breaking off. Are these two problems related? I guess that a boring insect is the cause. How can I rid my trees of these problems?
ANSWER: The problems you have observed on your Arizona cypress trees are two different insects. Both are aggressive pests of cypress and junipers in Arizona. The first is the western cedar borer (Trachykele blondeli Marseul). It belongs to the buprestid beetle group also known as metallic or flatheaded wood borers. Unlike most other buprestids, this borer will attack and seriously injure or kill seemingly healthy trees. Considerable damage is found in some juniper stands; older, larger trees seem to be favored by the beetles. Adults range from 1/4 to 1/2 inch long and are bright emerald with several dark areas on the wing covers. Females lay eggs under bark scales on branches of living trees. Flatheaded larvae bore from branches in to the main trunk where they feed on the heartwood for several years. Mature larvae move near the surface and pupate. Adults emerge in the spring leaving oval or rectangular exit holes. The second insect is the juniper twig pruner (Styloxus bicolor (Chamlain and Knull)). Juniper twig pruner causes twig dieback on the tips of tree branches. The insect is a small cerambycid or long-nosed beetle. The juniper twig pruner adult is 1/4 to 1/2 inch long and has a redish-orange head and brownish to black body. Eggs are laid on branches, often near an intersection of twigs, one to two feet from the branch tip. Larvae are small, white, cylindrical, legless grubs that kill twigs by boring through the centers. The life cycle may take as long as two years to complete.
Control: No practical controls or preventive measures have been developed for western cedar borer. Control of juniper twig pruner is unavailable also. Chemicals are not registered for this pest. Damage can be unsightly when populations are high but trees are rarely seriously injured by the juniper twig pruner. However, the western cedar borer will kill your trees.
Source: Conifer Pests in New Mexico, Robert Cain, Jesus Cota* and Charles Ward. 1990. New Mexico State University - Cooperative Extension Service and *USDA Forest Service, pp. 32-33.