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Why hull split is a critical time for navel orangeworm control

Suterra Jul 24, 2023 4:09:56 PM

With hull split approaching, protecting this season’s almond crop from navel orangeworm (NOW) damage is a top priority. What is in your sprayable toolkit for 2023?


Why is hull split timing critical for NOW management?

Before hull split, navel orangeworm infestations primarily occur on mummy nuts. The current season’s crop becomes highly susceptible to damage caused by navel orangeworm after hull split. When almond hulls split, they release volatiles that attract gravid females to the nuts, where she will lay her eggs. Newly emerged larvae enter the shell and feed on the kernel, causing significant damage and increasing the risk of aflatoxin contamination.

When using selective insecticides at hull split, spray timing is critical to target the early-stage larvae when they are small and most vulnerable and before they have entered the protected environment of the almond shell. Effective hull split sprays should attempt to thoroughly cover all exposed parts of the hull and shell to maximize the likelihood that the larva will contact the insecticide residue as it attempts to make its way into the kernel.

Hull split is not an immediate process, occurring over a period of weeks leading up to harvest. Suterra’s Dr. Emily Symmes explains the challenges associated with hull split insecticide applications. “As the hull opens more each day, increased surface areas of the interior of the hull and the shell are exposed, and these newly exposed tissues are not protected by the insecticide residue. Female NOW moths are adept at positioning their ovipositors (egg-laying ‘tube’) to deposit eggs as close to the larval resource as possible, often avoiding the plant tissues covered with insecticide. In this case, the larvae will not die and will enter the kernel resulting in crop damage.”

To maximize crop protection between hull split and Nonpareil harvest, many operations choose to apply two hull split sprays (typically 2 to 3 weeks apart) to keep insecticide residues on as much of the exposed plant tissue as possible. Because of these challenges, the industry consensus is that even the most optimized hull split insecticide sprays (proper timing and adequate coverage at the time of application) each provide 50% efficacy at best.

What is available in the sprayable toolkit for NOW?


Hull split timing can be predicted using full bloom timing paired with temperature data, which can help growers and their pest control advisers plan their spray timing(s). It is important always to confirm hull split model predictions with in-field observations of hull split in each block. “Due to the cooler, wetter spring, and this year’s prolonged bloom period, we may end up with a more staggered hull split period, further complicating the efficacy of hull split insecticide sprays. That is where integrating sprayable pheromones into the program will add significant value,” according to Dr. Emily Symmes.

While often an important tool for helping protect the crop, insecticide sprays alone may not be sufficient to achieve the industry standards for low navel orangeworm damage. Using CheckMate® NOW-F sprayable mating disruption in a tank mix with one or more hull split insecticide applications or as a stand-alone treatment will provide additional, flexible protection to complement the insecticide program.


What are the benefits of CheckMate® NOW-F?

Suterra’s proprietary microencapsulated CheckMate® formulations are engineered to release pheromone consistently in all environmental conditions for a period of up to 30 days following application. Unlike insecticides, contact with or ingestion by the target pest is not required, meaning that full coverage is not necessary for efficacy. In addition, the long residual activity does not require the precision timing of selective pesticides.

“Because the mode of action is mating disruption, we only need to get uniform distribution of CheckMate® NOW-F into the orchard environment. Each microcapsule acts as a microscopic pheromone dispenser, and once the active ingredient is released and becomes airborne, it will contact the male antenna to inhibit his ability to find females to mate with,” explains Dr. Emily Symmes.

CheckMate® NOW-F sprayable mating disruption is tank-mixable with most common agrochemicals and has zero pre-harvest interval, allowing growers the flexibility to add sprayable pheromones to existing programs and protect the crop up to harvest of each variety and beyond.

There are many versatile approaches to incorporating sprayable mating disruption into your navel orangeworm IPM program, and our technical team is happy to help. Contact us here, and we will connect you with a Suterra expert in your area.


This article is focused on the use of CheckMate® NOW-F during the hull split period. It is not meant to recommend a specific spray program (number of sprays, spray timings). Like any sprayable pest management input, the number of CheckMate® NOW-F applications, spray timings, and application methods should be decided in consultation between growers and their crop advisers.