Ask Your PCA: When and how should Ethephon be applied in walnuts?

By Justin Nay
Integral Ag Services, Durham

In late August, Chandler walnuts begin the “packing tissue brown,” or PTB, stage, which refers to when the tissue surrounding the kernel halves turns brown, indicating the kernel is at peak maturity and growers can begin harvest. Once orchards reach 100% PTB, a window opens for applying Ethephon. 

Ethephon is a spray application that accelerates natural husk split and lets growers harvest about two weeks early. Using Ethephon can also help maintain kernel quality and increase the chances of delivering more kernels to the processor at premium color grades.

Sometimes more nuts are shaken from the trees than the walnut dryer can handle. Depending on availability of dryer space, spreading out the harvest reduces pressure on the dryers. Larger growers often use Ethephon for a more even harvest pattern, allowing them to use labor, equipment and dryer time more efficiently. An earlier harvest also means avoiding even greater late-season pressure from navel orangeworm, or NOW. 

Growers noticed the third flight of NOW in August, and the fourth flight has begun. In addition, if almond or pistachio pollinator varieties are located near walnut orchards, there can be significant late-season navel orangeworm pressure as Chandler husk split begins. A later harvest exposes nuts to more NOW activity and increases overall risk.

Things to be aware of when making an Ethephon application:

• Apply during cooler weather for best results.

• Avoid overapplications to prevent defoliation.

• Wait for 100% brown packing tissue before applying.

Choosing between an earlier harvest or another insecticide application often comes down to cost, yet predicting NOW pressure is never certain. An Ethephon application that enables early harvest may avoid the need for additional sprays and preserve quality.

Given the level of NOW pressure observed this year, harvesting sooner rather than later could make strong economic sense for many walnut growers across affected districts.