Control of Navel Orangeworm in Almond, 2019

This study evaluated the efficacy of reduced risk insecticides for NOW control. The study was conducted in an almond orchard near Manteca, CA. Five treatments and an untreated check were replicated four times in an RCB design, each replicate being a single tree. Two replicates were on an inside row of the orchard, and two were on an outside row. The two rows were both nonpareil with a pollinator row in between. The orchard was planted with 22 ft row × 20 ft tree spacing. Materials were applied with a hand-held orchard sprayer operating at 200 psi with a finished spray volume of 150 gal/ac. NOW were monitored with two egg traps and pheromone traps. Traps were placed in the orchard on 19 Jun and the traps were monitored weekly until 5 Sep. Treatments were applied to the outside row on 10 Jul at the beginning of hull split (5% or less) when eggs were present on NOW egg traps and moths were captured in pheromone traps. A second application was applied on 23 Jul. Treatments were applied to the inside row on 16 Jul at the beginning of hull split (5% or less) when eggs were present on NOW egg traps and moths were captured in pheromone traps. A second application was applied on 30 Jul. The applications occurred during the second flight, with the third flight beginning two weeks after the last application. Due to grower equipment limitations, harvest was delayed and did not occur until 10 Sep. Shortly after harvest (shaking) on 10 Sep, 250 nuts per tree (1,000 nuts/treatment) were picked up from the ground before windrowing and inspected for NOW. Infestation was classified as none, larvae present (predominantly third-generation larvae originating from the third flight) or larvae absent (predominantly second-generation larvae originating from the second flight that already pupated and emerged before evaluation). Data were analyzed using ANOVA and means separation with Fisher’s protected LSD (P < 0.05).

All treatments reduced the percentage of nuts infested by second-generation larvae (NOW absent) compared with the untreated check, and there were no significant differences among experimental treatments (Table 1). There were no significant differences in the percentage of nuts with live larvae (NOW present), likely because eggs for these larvae would have been laid two or more weeks after the second application was made. All treatments except for Altacor 35WG had significantly lower percent NOW total compared with the untreated check. Intrepid Edge had significantly lower percent NOW total infestation than Altacor 35WG, and there were no significant differences among the other treatments.¹

Footnotes