Evaluation of insecticides at hull split for navel orangeworm in almonds, 2024

Navel orangeworm (NOW) is a significant pest of almonds due to the ability of larvae to penetrate through the shell and feed directly on the harvestable kernel. Kernels infested by NOW are also at increased risk of the presence of aflatoxins that are highly regulated in certain export markets. In this trial, we evaluated the effects of 3 untreated checks and 17 insecticide treatments, when applied twice during a 2-week interval starting at the initiation of hull split, on the percentage of nuts infested at harvest. This trial was located in the pollinator variety Monterey with insecticide applications targeting the third flight of NOW.

The trial was organized as a CRD with 6 replications of 2-tree plots in an experimental almond orchard maintained by the University of California in Kern Co., Shafter, California. The orchard was planted in 2009 using a 20 ft by 22 ft spacing of alternating rows of the varieties Nonpareil and Monterey. Applications were made to the variety Monterey on 1 Aug and 14 Aug, to span the third NOW flight, with the first application timing coinciding with the initiation of hull split. Applications were made using a gas-powered wand sprayer calibrated to deliver 200 gallons of water per acre. All treatments were made with the inclusion of Dyne-Amic as a surfactant at a rate of 32 fl oz/acre (0.125% v/v).

Nuts were harvested on 11–12 Sept by placing a tarp under each tree and using a pole to knock down approximately 300–500 nuts, with care taken to collect from all elevations within the tree. Nuts on the tarp were gathered, mixed, and a subsample of approximately 250 to 300 nuts per tree was placed into a paper sack. The sacks were placed directly in the freezer for future processing. In November, all nuts were cracked open and recorded for NOW damage. Data of the percentage of nuts with damage were evaluated by ANOVA with means separated by Fisher’s Protected LSD (α = 0.05).

Industry-standard insecticides containing methoxyfenozide or chlorantraniliprole (Intrepid, Intrepid Edge, Altacor) significantly reduced the percentage of infested kernels to < 68.6 compared to > 79.1 in the three untreated checks (Table 1). Significant reductions were also seen for the higher rates of the experimental products Plinazolin and LX161. Use of Verdepryn and Brigade resulted in damage levels that were statistically reduced compared to 2 of the 3 untreated checks to levels that were statistically equivalent to some of the industry standards. Statistically significant reductions were not seen compared to any of the 3 untreated checks for Steward or for treatments containing the microbial products Spear-Lep + Leprotec, or MBI-306 (Onira EP). Another microbial product, BasinFlex, when combined with the Bacillus thuringiensis product Javelin, reduced damage compared to 2 of the untreated checks, but only to levels equivalent to when Javelin was applied by itself.¹

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