Ask Your PCA: What are economical ways to manage walnut pests?

By Justin Nay

Integral Ag Services, Durham

Walnut prices have been down for several years, so finding ways to reduce costs remains a priority for many growers.

Codling moth overwinter as full-grown larvae in silken cocoons under loose scales of bark. Moth emergence usually coincides with the leafing out of early walnut varieties. 

Codling moth is a damaging pest in walnuts, and the amount of damage varies with each generation. The first generation larvae reduce yield by directly causing nutlets to drop. Damage from the end of the first generation and the second and third generations is due to feeding damage of the kernel. The damaged nuts also become a breeding site for navel orangeworm, or NOW. 

Good codling moth management in most scenarios can lead to good NOW management. Conceivably, growers could reduce treatments for NOW later in the season when the third and fourth flight arrive if codling moth is well managed earlier in the season.

If codling moth numbers are low, often NOW numbers will be low as well until husk split. But if there are neighboring almonds, there could be an influx of NOW when almond harvest begins. 

Codling moth treatments include mating disruption, biological control and chemical treatments.

Some growers have been using pyrethroids on codling moth to reduce expenses. Another option could be Intrepid or Altacor. While these chemicals may cost a little more, there could be better results because the residuals last longer than a pyrethroid on the later codling moth flights. 

The later flights are typically the ones in which more navel orangeworm get into nuts because the nut meats are mostly formed and the navel orangeworms live inside the nuts after the codling moths exit. 

The bottom line: A strong investment on the codling moth treatments could result in less NOW later in the season and fewer treatments for NOW. This could ultimately reduce costs.