Pacific flatheaded borer

Damage from the Pacific flatheaded borer, Chrysobothris mali, often can be seen in late August and September in shade tree production. The following images were taken during August of flatheaded borer damage and larvae on cherry and plum trees. Adult borers emerge from late May-June and are reported to fly for about one month.

Insecticides are not always recommended for this pest in field nursery production. Rather many growers in field-grown production rogue out and burn thoroughly infested material. Container shade tree producers are more apt to make protective applications, given the higher investment costs associated with those trees.

Monitoring for Pacific flatheaded borers is generally done with colored traps for these visually-oriented beetles (as opposed to the use of pheromone or ethanol traps). Purple-colored sticky traps have been used for Buprestid beetles such as flatheaded borers and emerald ash beetle. The use of traps help to determine the flight of the adult beetles. Awareness of the flight, may help with timing of protective applications and scouting for injured trees and localized pockets of damage.

If possible, determine if there have been causes of stress to the trees. Drought stress, sunburn, flooding, and tree wounds are some of the underlying factors making trees susceptible to flatheaded borer damage. Trees adjacent to natural wooded areas with weakened trees that might host the beetles, may also be more susceptible.

Oregon State University Pacific flatheaded borer fact sheet

Forest Pests of North America: Pacific flatheaded borer

Original version: <2 September 2003)

Last update <29 December 2016>

Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.