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Walnut

Identifying Seasonal Pests 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

Naval orangworm
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
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
Ants

Tunnels chewed into the kernel.

No

No

No

Ants feed in groups.

 

Walnut husk fly
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
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.


Statewide IPM Program, Agriculture and Natural Resources, University of California
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