Pistachios Suffer Navel Orangeworm Damage
November 8, 2017
Overwintering NOW Population Must Be Reduced
By Robert H. Beede, UCCE Farm Advisor, Emeritus
The following is a special report by Robert H. Beede, UCCE Farm Advisor, Emeritus, on the state of the pistachio harvest and the fight against navel orangeworm damage.
Season Wrap Up: It looks like we wound up with about 600 million pounds. Only God knows how many million navel orangeworm got, but you all know it was a bunch! Processors have their hands full delivering the quality nut California is known for. Many growers I speak to ask, “What happened?” From my discussions with many crop consultants, what DIDN’T happen was sanitation! This was not only true for the pistachio growers, but almond producers as well.
Growers barked at me about the wet weather making orchard access difficult to impossible, the size of the trees making sanitation cost prohibitive, and the difficulty in getting the nuts out of the trees. These issues are all true. So, if you decide that you cannot sanitize, then you had best figure out how you are going to run the ranch on pistachios that are 30 to 40 cents less valuable than those with low worm damage.
I know I sound like the donkey’s behind with all the answers, but the pistachio industry needs to join forces with the almond guys to determine what we can collectively do to reduce the overwintering NOW population.
There has been millions spent studying NOW, and I have NEVER waivered on the fact that sanitation is the cornerstone to controlling this beast! I also still think that once we get the kinks out of mating disruption, that everyone should use it as a means to SUPPRESS the population. Note that I did NOT say, “Control it as a stand-alone program," just in case someone out there wants to stuff words in my pie hole!
We are in DESPERATE need of an effective adult monitoring tool for NOW mating disruption. I hope this comes soon, in order to give pest managers a method of knowing when the pheromone is not reducing mating sufficiently. We also need more research on the cultural and environmental factors affecting the number of early split nuts, which become the NOW link to the new crop at harvest.
Sanitation: Now is the time to begin winter sanitation by removing the nuts that did not come off during harvest. Many of these nuts are blank, but do not assume that all of them are. Research by many good scientists has proven that winter sanitation is the key to breaking the overwintering NOW population cycle, which looms ever greater when the winter is warm and dry. Beginning the season with a large overwintering population simply reduces the effectiveness of your in-season sprays. Although the research has not been done, to my knowledge, the TIMING of sanitation may be a factor in its efficacy.
Nut removal and destruction early in the fall may be more effective, because the percentage of NOW larva in the early instar stages should be greater. This is due to the large peak in egg laying that occurs during hull degradation. Thus, they may be more susceptible to desiccation or fungal attack because of their smaller size. Disturbing their overwintering site from the tree onto the ground early also places more environmental pressure on their survival. This is just my opinion; it may be worthy of investigation.