Tips for Selecting, Applying Navel Orangeworm Hullsplit Sprays

With final harvest preparations top of mind, growers may be considering spray applications to continue keeping navel orangeworm (NOW) at bay and protect their crop. Growers should work with their PCAs to determine if sprays are necessary based on trap monitoring along with flight calculations based on egg traps. Effective hullsplit sprays are difficult in order for good control to occur the material needs to reach the sutures of the nuts, and hullsplit can take 3-4 weeks to complete in a variety. Here’s a few things to keep in mind to improve the efficacy of hullsplit sprays a few things to keep in mind:

1. Timing

• Timing should coincide with the beginning of hullsplit and NOW’s second flight.
• The first spray should be completed at no later than 1% hullsplit.
• To predict the onset of hullsplit, reference the Almond Hull-Split Prediction Model created by Ted DeJong of UC Davis’ plant sciences department.

2. Chemistry

• Assess the potential risks of the compound to beneficial organisms and environmental quality. NOW control should work in tandem with other IPM strategies, and some materials can decimate thrips that are working hard to control spider mites.

3. Sprayer Calibration

• Given the difficultly to reach the sutures of the nuts, take the time for ensure the sprayer is properly calibrated to effectively reach the tops of the trees.

4. Volume

• Growers and applicators should apply the proper volume of spray material to ensure full coverage. Consult a PCA to determine the correct volume, but research suggests 200 gallons per acre as a rule of thumb to maximize effectiveness.

5. Speed

• Research funded by the Almond Board of California (ABC) and others shows that proper sprayer speed and spray volume are often overlooked during hullsplit, even though research repeatedly shows that slowing down improves coverage.
• Sprayer speeds should remain at the recommended 2 miles per hour to ensure better coverage.

6. Repeat

• Work with a PCA to assess any existing or potential crop damage after the first spray application to determine if another application is needed.

While this IPM approach to NOW control is tried and true, ABC continues to invest in research to find even more options to combat NOW. This spring, the Almond Board approved its largest-ever production research project — to the tune of $1 million — that seeks to learn more about using the Navel Orangeworm Sterile Insect Technique in almonds. This effort to continue advancing and evolving IPM tools supports the industry as it charges toward the Almond Orchard 2025 Goal of increasing the adoption of environmentally friendly pest management tools by 25% by 2025.