Individual and additive effects of insecticide and mating disruption in integrated management of navel orangeworm in almonds

Authors: HIGBEE, BRADLEY - Trece, Inc; Burks, Charles - Chuck

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2021
Publication Date: 2/22/2021
Citation: Higbee, B.S., Burks, C.S. 2021. Individual and additive effects of insecticide and mating disruption in integrated management of navel orangeworm in almonds. Insects. 12(2):188. https://doi.org/10.3390/insects12020188.
DOI: https://doi.org/10.3390/insects12020188

Interpretive Summary: The navel orangeworm is the most important insect pest of almonds, which are planted on 1.5 million acres in California and worth $5.5 billion annually. Mating disruption for navel orangeworm is used on 500,000 acres of tree nuts, but this environment friendly practice can still be expanded and optimized. Analysis of damage data from a decade-long area-wide research project revealed that the effects of mating disruption and commonly-used selective insecticides are additive. Use of insecticide with mating disruption had a stronger effect than increasing the intensity of mating disruption. Year-to-year variability in overall damage, and in the proportion of damage in earlier- vs. later-harvested almond varieties, demonstrated the difficulty in predicting navel orangeworm damage. These findings will help growers to optimize the economic return from mating disruption, and demonstrate the challenge in meeting the almond industry goal to reduce insecticide input by 25% between 2020 and 2025.

Technical Abstract: Damage from Amyelois transitella, a key pest of almonds in California, is managed by destruction of overwintering hosts, timely harvest, and insecticides. Mating disruption has been an increasingly frequent addition to these management tools. Efficacy of mating disruption for control of navel orangeworm damage has been demonstrated in experiments that included control plots not treated with either mating disruption or insecticide. But the navel orangeworm flies much farther than many orchard pests, so large plots of an expensive crop are required for such research. A large almond orchard was subdivided into replicate blocks of 96 to 224 ha and used to compare harvest damage from navel orangeworm in almonds treated with both mating disruption and insecticide, or with either alone. Regression of navel orangeworm damage in researcher-collected harvest samples from the interior and center of management blocks on damage in huller samples found good correlation for both and supported previous assumptions that huller samples underreport navel orangeworm damage. Blocks treated with both mating disruption and insecticide had lower damage than those treated with either alone in 9 of the 10 years examined. Use of insecticide had a stronger impact than doubling the dispenser rate from 2.5 to 5 per ha, and long-term comparisons of relative navel orangeworm damage to earlier- and later-harvested varieties revealed greater variation than previously demonstrated. These findings are an economically important confirmation of trade-offs in economic management of this critical pest. Additional monitoring tools and research tactics will be necessary to fulfill the potential of mating disruption to reduce insecticide use for navel orangeworm.