Given its persistence and potential for crop damage, navel orangeworm is no longer just another problem that can arise; rather, it’s a problem that will arise, and management must be thought of as a proactive annual program like fertilizers, harvest or pre-emergent herbicides.
That was the message at a recent webinar on Getting the Most Out of Your Navel Orangeworm Program. Peter McGhee, an entomologist with Pacific Biocontrol, outlined the key fundamentals of an efficient NOW management program and how best to incorporate pheromone mating disruption. He was joined by independent PCA Carla Youngblood and nut grower Chris Wylie with Wylie Farms.
Four key fundamentals of an efficient NOW management program, according to McGhee, are sanitization, monitoring (traps and nut surveys), sprays and mating disruption. NOW is active all year and has “no significant diapause,” McGhee said, meaning that growers can simply not lag in any of the four fundamentals of management.
Pheromone mating disruption is the key to proactive NOW management. When paired with the other key fundamentals, it is the cherry on top that works nonstop.
In the ways that fertilizers, pre-emergent herbicides and securing early labor for harvest can be thought of as proactive, NOW disruption can be thought of in the same way. Growers should be proactive about NOW in order to mitigate its impact in the orchard, McGhee said.
Mating disruption works by interfering in the natural reproduction of NOW adults to limit future generations.
“Insects such as NOW have odors, sort of like perfumes, that they produce in order to attract a mate,” McGhee said. “The female NOW sits high up in a canopy producing these pheromones, and males fly back and forth through the orchard trying to detect pheromones in the wind. What we can do to disrupt this is deploy synthetic pheromones from aerosol emitters or other devices that attract the male instead.”
Pacific Bio’s Isomate Mist synthetic pheromone emitter is registered for use in almond, pistachio and walnut orchards, emitting a pheromone plume more than a thousand times more powerful than a female NOW plume, McGhee said.
“The male NOW flying through the orchard is going to find that large, more concentrated pheromone plume,” McGhee said. “He’ll either fly to the mechanism [emitter] itself or he will shut down and won’t respond at all.
“Either way, what’s happening is you wind up with a female that’s not mated or she might be delayed,” he continued. “That’s really important because moths are short-lived and mating occurs within the first two days. If we can delay or stop that mating within the first two days, then the female can produce up to 70% less fertile eggs than normal.”
Emitters are deployed at a rate of one unit per acre. Deployment should begin at the start of April, and the emitters should last until the end of October or beginning of November depending on temperatures in a given season, McGhee said. The emitters also have temperature sensors that will shut the emitter off if it detects that it is too cold for NOW to be active.
“[For deployment], we use ATVs and Gators, and I have four or five men that cover about 3,100 acres in five days,” Wylie said. “We deploy in patterns of ten rows by ten trees. It’s not really a big task. I figure it’s probably less than $10 per acre.”
Wylie said that the overall reduction in pest damage covers the cost, and believes use over time will allow growers to eliminate an insecticide spray, further cutting costs.
“In the first year, we did not [cut out insecticides],” Wylie said. “In the second year, we thought about it but were a little reluctant. In the third year, we did remove one application and still continued with normal management practices like sanitation.”
“In the first year, I wouldn’t recommend cutting out any insecticides,” Youngblood agreed. “After the second year of mating disruption, I have cut out NOW sprays as we did feel like we had good control.”
While growers will see steady reductions in NOW infestation numbers ̶ a 50% average reduction in the first year and steady reductions in following years, according to Youngblood ̶̶ even with an eventual reduction of insecticide usage, it is always important to stay on top of NOW management in general. Wylie said NOW is the most persistent and damaging pest for tree nut crops, so growers should stay vigilant using the key fundamentals of a management program.
“When it comes to mating disruption and sanitation, I’m not even going to think about slowing down over the next few years,” Wylie said. “It’s a terrible insect.”
Multi-Year Pheromone Study
In a recent Pacific Biocontrol study, two sets of four replicated blocks observed in 2019 and 2020 were treated with and without pheromones from ISOMATE Mist NOW emitters. Both block sets had male NOW traps set up to observe flight activity with and without emitters.
The block sets that were not treated with pheromones showed high activity spikes that deviated when reactive insecticide sprays were used, but spiked again when the sprays wore off. The block sets that were treated with pheromones showed little to no spikes at all.
“In the blocks that were pheromone-treated, the pheromone traps caught virtually no moths for both years,” McGhee said.
The study also looked at what this reduction in male NOW flight activity meant for egg laying and nut injury in both observation years. Eggs caught in egg traps were reduced by 47% from the grower standard due to pheromone usage in 2019 and by 75% in 2020. Nut injury was reduced by 76% from the grower standard in 2019 and by 80% in 2020.
“This is how we can proactively manage NOW, not just within one season but over multiple seasons, hopefully driving these populations down to zero or as close as we can get,” McGhee said.
Of course, these results are in conjunction with normal NOW management. Sanitization is necessary during every season, and targeting of multiple life stages with insecticides is necessary as trap counts dictate.
“Measure the result in years,” McGhee said. “There are no quick fixes [for NOW] anymore.”