Integrated Pest Management

Walnut Twig Beetle

walnut twig beetle

Walnut twig beetle (Walnut twig beetle, Steven Valley, Oregon Department of Agriculture, Bugwood.org)

walnut twig beetle

Exit holes produced by walnut twig beetles (Whitney Cranshaw, Colorado State University, Bugwood.org)

walnut twig beetle galleries

Walnut twig beetle galleries and cankers caused by Geosmithia morbida (Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org)

Pest Description

  • adults: 1/16 inch – 1/13 inch; yellowish brown; three times as long as wide
  • larvae: white grubs with a brown head capsule; no legs

Host Plants, Diet & Damage

  • walnut
  • feed on phloem
  • primarily attack walnut trunks and branches
  • cause yellow flagging in tree canopy or canopy dieback
  • introduce the pathogenic fungus Geosmithia morbida (“thousand cankers disease”)
  • kill or weaken susceptible walnuts, especially black walnut

Biology, Life Cycle & Damaging Life Stage

  • overwinter as larvae and adults
  • emergence begins in April
  • two to three generations per year
  • larvae and thousand cankers fungi introduced by adult beetles are the primary damaging stages

IPM Recommendations

  • Monitor closely for beetle activity, tree health, and thousand cankers lesions under bark.
  • Prune infected branches and remove from site.
  • Pesticides have very limited use in protecting trees from the beetle and fungus.
  • Infested trees should be identified as quickly as possible, removed, and debarked.
  • Do not transport walnut firewood.

For more information, see our Bark Beetles fact sheet.