Sure, you can harvest your walnuts this fall without application of any ethephon. Forgoing the ethephon application would save you material and spray costs. However, despite the costs of application, use of ethephon may wind up saving you money in the long run. Depending on your operational needs, ethephon can be used two ways: to increase kernel quality or to promote a one-shake harvest. Below are some factors to take into consideration while making your decision.
Cultivar considerations. You’ll get the biggest bang for your buck if your cultivars respond well to ethephon application. Tulare is extremely sensitive to ethephon, while Howard and Vina respond well. Serr shows only a marginal response. Many growers have successfully used ethephon to stagger Chandler harvests.
Promoting one harvest. A well-timed application can help remove most nuts at the first shake, saving you the expense of sending the harvest crew through the block a second time. Apply at 5 to 7 days after 100% packing tissue brown (PTB), approximately 10 days prior to the normal harvest date. This spray timing should remove most nuts in the first shake and avoid an uneconomical second shake.
Kernel quality. Using ethephon to advance harvest may result in nuts with lighter kernel color or lower insect damage, should a NOW flight coincide with hull split. High quality kernels will net you the best pricing. Apply when nuts first reach 100% PTB. The first harvest will be approx. 7-10 days earlier than normal; the second shake should occur 2 weeks later.
Operational considerations. When needing to harvest across many blocks, strategically spacing out applications among some blocks but not others can ensure harvest timing will be staggered and that equipment will be available at optimal timing.
Weather. Ethephon is most effective when applied between 60 ̊F to 90 ̊F and with higher humidity conditions. If the weather is predicted to be rainy, hot, or windy, ethephon efficacy is decreased, and you may not get the results you are expecting. Also, avoid using ethephon on stressed orchards.