Seasonal Pest Damage in Harvest Samples

Observe nut damage at harvest to identify pests that escaped your management program. Look for the presence or evidence of navel orangeworm, walnut husk fly, codling moth, and ants. Knowledge of the current year’s problems will help plan for next year.

Look through walnuts collected for the harvest sample. Use the photos below to identify pests (and sunburn) that cause damage. Names link to more information on identification and management.

Click on photos to enlarge

Photos of nut damage	Kernel	Frass	Webbing	Boring	Feeding behavior	Other
Navel orangeworm	Deep chewing into kernel.	White, often quite a lot.	Yes, often quite a lot.	Yes, into kernel.	Larvae feed in groups. Many per kernel.	Shells of heavily infested nuts appear oily.
Codling moth	Deep chewing into kernel.	Frass at point of entry into the husk.	Very little.	Yes, into husk and kernel.	Single larva feeds per kernel.	NA
Ants	Tunnels chewed into the kernel.	No	No	No	Ants feed in groups.
Walnut husk fly	Early season infestations may cause shriveled/ darkened kernel. Late season infestations do little kernel damage.	No	No	Yes, into husk.	Larvae feed in groups. Many larvae per husk.	Husks are blackened and shell is stained black. Husks cannot be removed cleanly from shell.
Sunburn	One side of the nutmeat darkened and shriveled.	NA	NA	NA	NA	One side of husk darkened and shriveled. Husks can be removed cleanly from shell.