Flatheaded Borers

Pacific flatheaded borer. Pacific Flatheaded Borer

Flatheaded borer damage.
Flatheaded Borer Damage


  • All fruit trees, especially stone fruits, apple, and pear
  • Many other woody plant species


The flatheaded apple-tree and pacific flatheaded borers are usually only a problem when trees are stressed by drought conditions or when populations are high in an area, such as a stack of infested firewood nearby. The larvae feed under the bark, and can kill young and stressed trees and those in decline. The adult beetles are active in June and July and lay eggs on the trunks of stressed trees.


Flatheaded borers overwinter as larvae inside the tree, and emerge as adult beetles in June-August (northern Utah). Adults lay eggs on bark crevices and the newly hatched larvae immediately bore through the bark to feed in the phloem layer.


  • Oval-shaped exit holes
  • Frass
  • Loose, dead bark
  • The larvae can eventually girdle trunks which will kill young trees and trees with multiple attacks.



Watch for adult beetles May-July.


  • Residential: imidacloprid (systemic), carbaryl, or permethrin
  • Commercial: Click Here

Precautionary Statement: Utah State University and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks, and not all are registered for edible crops. “Restricted use” pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed in this publication.