Walnut Twig Beetle
Walnut twig beetle (Walnut twig beetle, Steven Valley, Oregon Department of Agriculture, Bugwood.org)
Exit holes produced by walnut twig beetles (Whitney Cranshaw, Colorado State University, Bugwood.org)
- 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
- 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
- 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.