May/June 2025
Flight sync and field sanity
In California’s Central Valley, few pests are as elusive, costly and persistent as the navel orangeworm (NOW). For both almond and pistachio growers, controlling NOW is a critical factor in crop quality, marketability and long-term orchard profitability.
While most research and outreach efforts have focused on pest suppression within individual orchards, it’s becoming increasingly clear that a successful NOW program depends on mutual understanding and coordination between neighboring crops, especially almonds and pistachios.
The four flights and a shared ecosystem
NOW development is temperature-driven — usually measured in degree days — and typically follows four distinct flights each season. Each flight presents challenges and opportunities for almonds and pistachios.
Flight one: March to April
This early emergence targets remaining mummies from the previous season. Because almond harvest begins months before pistachio harvest, mummies that were not previously destroyed by winter sanitation can significantly increase the presence of NOW at Nonpareil hull split.
Almond spring spraying options for NOW control during this period can include pyrethroids for adults and larvae, and larvicide for larvae. Spray timing should be aligned with pest pressure. If tree mummy counts are high, sprays would be timed for NOW egg laying; if the mummy count is less than two per tree, sprays may target mites or disease later in the season.
Pistachios are coming out of dormancy at this point. Spring spray is usually driven by small plant bugs rather than NOW flight one, since pistachio tree mummies are typically removed from the tree much easier than almond tree mummies. Plus, infestation of ground mummies is less likely with pistachios. However, if timed well, spring spray can coincide with almond mummy sprays depending on the small bug presence, and pyrethroids used can also knock down emerging moths from the pistachio floor mummies.
Flight two: Late June to early July
During this flight, newly hatched larvae begin looking for developing nuts with entry points.
In almonds, this period overlaps with hull split in Nonpareils, Independence and other late flight two pollinators like Aldrich or Wood Colony. Growers typically treat twice with, at minimum, group 28 or 18 insecticides, and often pyrethroids.
Pistachios are still largely protected at this stage, as the hulls have not degraded and are not attractive to NOW. However, if other sprays are being made and can be timed to roughly 1,400 degree days or detection of flight two, a knockdown material can be used to kill adult moths.
Flight three: Late July to early August
At this point, Nonpareil have just hit the ground, and late varieties become vulnerable as NOW adults emerge from the fresh Nonpareil crop. Pollinator varieties with waning pesticide residue may also be vulnerable at this point, especially as growers await the removal of Nonpareil from the orchard. Some growers opt to spray pollinators only before shaking Nonpareil, while others spray after Nonpareil to maintain protection during this flight.
Meanwhile, pistachios are nearing kernel fill. The lion’s share of the crop remains resistant to NOW infestation, but occasional early or pea splits may be vulnerable. Some growers apply larvicidal treatments at this point, though research on the efficacy of this timing is lacking. Pyrethroids used for other pests may also reduce adult NOW populations during this flight.
Flight four: Late August to October
The final flight overlaps with pistachio harvests and can cause considerable damage if harvest is delayed into late September, as NOW adults are emerging from almond pollinators and early-split pistachios.
Treatments are made in August and often repeated at two-week intervals, depending on preharvest intervals and expected harvest timing. Pistachio NOW damage tends to increase halfway through the harvest season, especially during second shakes. Late-harvested pollinators like Monterey and Fritz are also vulnerable to damage and may require treatment between variety harvests.
Maintaining protection for both crops during this flight is key to reducing overwintering NOW populations that will impact the following year.
Sanitation: Mummy destruction timing
Whether in almonds or pistachios, sanitation is the foundation of NOW control. In both crops, cover crops and berm vegetation can interfere with sanitation efforts. Growers using cover cropping systems must plan mow-downs or disk passes with sanitation in mind.
Delays in destroying infested mummies — especially in cover crops — can lead to greater NOW emergence and reinfestation of tree mummies. This increases regional pressure for the entire season.
Precision spray timing: Efficiency and efficacy
Spray applications still play a critical role, but the days of calendar-based spraying are over. Growers and PCAs must use a combination of trap catches, biofixes and site-specific day degree modeling, all while monitoring crop development, to ensure precision spray timing.
Trapping at flight one is a critical starting point. Even if you don’t farm almonds, monitoring flight one is key to understanding regional NOW dynamics. Establishing a biofix during this period allows you to begin modeling future flights.
Typically, the interval between flight one and flight two is 1,050 degree days. However, almond hull split doesn’t always align with this number. That’s why solely relying on degree days is not enough. Spray decisions must also be based on direct crop observations. Poor timing during this window can increase NOW pressure on pollinators and pistachios. In order to appropriately time application for hull split, you must consider both degree days and crop development.
Degree day data can be accessed through CIMIS or private weather stations and modeling dashboards. Growers should regularly compare trap trends and predicted degree day thresholds with crop development to stay ahead of each flight.
Following the first spray window, continue tracking degree days and flight activity:
- Flight two to flight three: roughly 750 to 1,000 degree days
- Flight three to flight four: roughly 500 to 750 degree days
- After flight four, overlapping generations may occur every 500 degree days
A firm grasp of this progression — paired with careful observation of both almond and pistachio development — can greatly reduce NOW infestation risk.
One pest, one community
Almond and pistachio growers are in this together. NOW does not respect property lines. Effective management requires shared responsibility, better communication and more regionally coordinated efforts — especially during critical times like flight one emergence and flight three infestation.
As researchers continue to study NOW behavior and refine our understanding of its population dynamics, growers can act now by:
- Prioritizing winter sanitation and well-timed mummy destruction in both crops
- Timing sprays with trap and degree day data
- Participating in regional research, trapping and communication networks
- Coordinating insecticide rotation with neighbors to reduce resistance
The future of NOW management won’t be solved by one grower, one block or one crop. It will be solved when the industry recognizes that almonds and pistachios are two fronts of the same battle — and we win when we fight it together.
