Flatheaded borers

Flatheaded borers tunnel beneath bark of trees stressed by drought, mechanical injury, or poor growing conditions across Western Washington. You will see sunken areas on trunks and branches with frass and sawdust accumulation. Affected wood becomes discolored and weakened. These beetles attack already-declining trees; they exploit weakness rather than create it.

Maintain tree vigor through proper watering, especially during drought, to prevent stress that attracts borers. Avoid unnecessary wounding and prune branches properly to prevent damage. Remove and destroy infested branches or trees if possible. No chemical control is practical for established infestations. Plant appropriate species for your site to ensure long-term tree health and vigor.