Control of codling moth in walnuts, 2022

This study was designed to evaluate the efficacy of rotations of reduced-risk insecticides for CM control. The study was conducted in an untreated ‘Payne’ walnut orchard near Vernalis, CA. Six treatments and an untreated check were replicated 4 times in a RCB design. Each replicate was a single tree and each treatment was a multi-spray program containing a rotation of 2–4 different insecticides. The orchard was planted with 22 ft × 44 ft offset spacing. Materials were applied with a hand-held orchard sprayer operating at 250 PSI with a finished spray volume of 250 gal/acre. Applications were based on degree-days (DD). DD were calculated using a single sine horizontal cutoff model with a lower threshold of 50°F and an upper threshold of 88°F. Maximum and minimum air temperatures were obtained from the Modesto A CIMIS #75 weather station in Stanislaus County, CA. The CM population was monitored weekly from 4 March through 21 September by placing 2 pheromone traps high in the tree canopy. Biofix was set on 22 March for the first CM generation and 9 June for the second CM generation. CM-infested dropped nuts were monitored weekly from 17 May through 15 June. CM and NOW infestation were determined based on 125 nuts per replicate (500 nuts per treatment) at commercial harvest on 20 September. Data were analyzed using ANOVA and means were separated using Fisher’s protected LSD (P ≤ 0.05).

The untreated check had significantly more dropped nuts compared to all experimental treatments, which did not differ among treatments Table 1. At harvest, the untreated check had significantly higher mean percent CM and NOW infested walnuts compared to all treatment programs. Damage levels in programs that began with Delegate were significantly lower than all other experimental treatments. All programs that included Shenzi 70WG had significantly lower damage than the grower standard programs exclusively using Altcor 35WDG, Delgate 25WG, and Warrior II. Significantly lower mean percent CM and NOW infested walnuts were observed when Delegate 25WG was applied for the first generation and Altacor 35WDG or Shenzi 70WG was applied for the second generation compared to when Altacor 35WDG or Shenzi 70WG was applied for the first generation and Delegate 25WG was applied for the second generation. The first 4 applications were timed for CM control and not for control of NOW. However, NOW often infests previously infested nuts by CM and the combination of both CM and NOW infestation reflects the best overall efficacy of the insecticide treatment regimes.

This research was supported by industry gifts of pesticides and research funding.