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 with an early harvest or to promote a one-shake harvest which can be economical in a lower price year. Below are some factors to take into consideration while making your decision.
Kernel quality. Using ethephon to advance harvest is primarily used to maintain lighter kernel color in nuts. Another advantage may be 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% packing tissue brown (PTB, see photo). This advances walnut harvest by four to seven days; the second shake should occur 2 weeks later.
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. Here, ethephon is applied about 10 days before normal harvest. Even applying ethephon five to seven days after PTB still improves percent nut removal and the chances of having to only harvest once, avoiding an uneconomical second shake.
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. To maintain lighter kernel color on the newer, early harvested variety Solano, lower rates of ethephon are advised until its response is researched and better understood. Look for PTB in August on early leafing varieties and in September on Chandler.
Operational considerations. When needing to harvest across many blocks especially with Chandler, strategically spacing out applications among some blocks but not others can ensure harvest timing will be staggered and that equipment and dryer space 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.