Walnut Husk Fly

A Serious Pest of both Walnuts and Peaches

  • An invasive species that originated east of the Rockies
  • Known to damage more than 2,000 species of plants and trees
  • Now found in California and the Pacific Northwest
  • Primarily a pest of walnuts, but also attacks peaches

The Walnut Husk Fly produces one generation per year and overwinters in the soil beneath trees. It is a mid to late season pest. In walnuts, females deposit eggs in the husk. After hatching, maggots feed inside the husk staining the nutshell. Later infestations result in shriveled, darkened kernels that are susceptible to mold and other environmental stresses which ultimately lower yield and quality.

In peaches, larvae feed internally on the fruit rendering it unmarketable.

Yellow Rectangle Trap

For effective intervention, it is necessary to monitor Walnut Husk Fly population levels. In general, constant monitoring is recommended. Contact local extension resources for specific regional recommendations regarding pest management strategies and control options.