Arborvitae (Thuja)-Borer

Western cedar bark beetle (Phloeosinus punctatus)

Flatheaded cedar borer (Chrysobothris nixa)

Shothole borer (Scolytus rugulosus)

Pest description and damage Beetle borers are pests of many different trees and shrubs. The 0.5-inch cedar borer adults are either brown to metallic gray or black with a red or orange sheen, depending on species. The larvae are whitish to pale yellow grubs about 0.5-inch long when fully developed and bore within the wood and bark of host plants. Just back of the larval head is a broad, flat enlargement giving the larvae a flat-headed appearance. Bark beetle (including shothole borer) adults are brown beetles less than 0.08-inch long. Bark beetle larvae feed just beneath the bark on the trunk leaving characteristic engravings. The damage may girdle the trunks and branches of trees leading to death of tissues distal to the damage. Holes made by feeding beetles may be associated with weeping sap on the trunk. Young, recently planted trees are most susceptible as are trees that are stressed due to drought or other plant stresses.

Pest monitoring Watch for watersoaked areas, depressions in the bark or cracks through which frass may be seen.

Management-biological control

Birds peck the larvae from under the bark. Some wasp parasites attack the borer. Carpenter ants eat both larvae and pupae from the wood, but may in turn colonize and expand borer tunnels into galleries for their nest.

Management-cultural control

As the adult borer is attracted to weakened trees, the best control is to keep trees healthy. Larvae cannot thrive in trees that are vigorous and full of sap. Avoid wounding plants, and follow good pruning, watering, and fertilization practices. To prevent sunburn, paint the trunk with white latex paint. Keep weeds, grass, and trash from the base of the trees to make it easier to detect and remove borers.

Management-chemical control

See Table 4 in: