Overall the first flight of navel orangeworm (NOW) has been lighter than normal this year. This could be attributed to relatively low 2018 damage levels, especially in pistachios, and the cooler, wetter weather during the 2019 spring.
“If we get really warm sustained temperatures early in the spring, navel orangeworm wakes up early and becomes active,” according to David Haviland, University of California Cooperative Extension (UCCE) entomology farm advisor for Kern County.
But this spring was cooler, overcast and wet, so the first flight was more spread out than normal, Haviland said.
“Damage last year in almonds was fairly typical, but in pistachios it was extremely low,” Haviland continued.
Less damage at harvest means lower infestation rates in mummy nuts that carry over to the next year.
“That’s a positive,” Haviland said.
A very low year for pistachio damage benefits other nut crops that might be growing next to pistachios, particularly in the southern valley, Haviland said.
Almond orchards next to pistachios normally have greater concerns about navel orangeworm because it’s much more difficult to sanitize pistachios than almonds.
“It certainly can be done, and it is done, but it’s more difficult to get them out of the trees and destroyed,” Haviland said, adding that it’s difficult to destroy pistachio mummy nuts on the ground because mowing them is like trying to mow marbles.
“When you’re dealing with overwintering populations there are two factors. The first is, how many mummies are left in the tree and on the ground that aren’t destroyed, but also what percentage of all of those mummies are infested,” Haviland said.
“So, generally speaking, the percentage of mummies infested this last winter was low because we’re following a low damage year, particularly in pistachios,” Haviland said.
“Sanitation continues to be an extremely important part of navel orangeworm management, however, sometimes it’s not possible to sanitize to the optimal level,” Haviland said.
This could be due to factors like: extremely tall trees, nuts that are stuck really tight, or increased labor costs.
“Increased labor costs have driven up the costs of sanitation,” Haviland said, and besides increased costs, finding labor can also be a challenge.
“Obviously if it costs more and more to do the same amount of sanitation, at some point you’re going to get people that decide they have to draw the line somewhere, and that’s happened in some cases,” Haviland said.
“We don’t want to encourage that, but that’s the reality as labor costs for sanitation come up,” Haviland said.
The trend is when there is really bad damage from NOW one year, the focus is to spend a lot of money on sanitation. When there is minimal NOW damage the reverse happens, and the tendency is to pull back on sanitation.
“That’s not what we would call ideal in terms of IPM (Integrated Pest Management), but is certainly a natural behavior,” Haviland said.
IPM Approach to NOW
“Sanitation is the core foundation, and on top of that we have insecticides,” Haviland said.
“Insecticides play an important role. One or two applications are common,” Haviland said, adding they are certainly important at hull split and a couple of weeks later.
Early or timely harvest is also important.
“We know that every extra day that the nuts are in the field creates an increased risk of navel orangeworm damage. The damage simply goes up day by day. We obviously have to wait until the nuts are ready to be harvested, but as soon as that date occurs, prompt removal of those nuts will reduce damage levels,” Haviland said.
“The other sort of newer technique that has increased significantly in the last few years is the use of mating disruption. Most mating disruption products are season long products that are put in the field around April and disrupt mating through harvest,” Haviland said.
“We’ve done a lot of work on mating disruption. We have a lot of really good data on the benefits it can provide. When used on 40-acre orchards, all four mating disruption products we tested from Suterra, Semios, Trécé and Pacific Biocontrol provided a 47 percent reduction in navel orangeworm damage. When we increased the scale to 100 acre squares or rectangles, reductions in damage over two years averaged between 50 and 70 percent,” Haviland said, noting that these results are from six demonstration orchards in the Southern and Northern San Joaquin Valleys.
Haviland continues, “But we also have the economic side of it. We know that the economic benefits of using mating disruption more than cover the costs to use it. In fact, over the past two years, grower returns in our trials increased by more than twice the amount that mating disruption cost. Reductions in damage should also be associated with decreased risk of aflatoxins in harvested nuts and increases in the ability to market ‘sustainability’ in the way almonds are produced. Mating disruption is sort of the leading edge right now,” Haviland said.
“There’s also a newly-registered option this year of a sprayable pheromone that can be added to the tank during hull split sprays,” Haviland said, noting that efforts are underway in 2019 to generate third-party data about whether or not the sprayable product is effective.
Sterile insect technique (SIT) is also being researched to determine whether or not it can provide additional benefits within an IPM program, Haviland said.
Both the pistachio and almond industries have made significant investments in this area. Currently, researchers in Arizona are trying to figure out how to mass-produce the navel orangeworm, sterilize them, and release them in a way that maintains normal moth behaviors.
If that hurdle is overcome, researchers will begin doing work to determine if they are effective, how many it takes to be effective, and whether or not the benefits outweigh the costs.
The Future for NOW Management
“There is absolutely no silver bullet for navel orangeworm, and there are no new chemicals coming down the pike. Management requires an integrated approach with multiple techniques,” Haviland said.
“The most successful growers routinely are the ones that integrate sanitation with insecticides and mating disruption while harvesting as soon as possible,” Haviland said.