Evaluation of insecticides at hull split for navel orangeworm in almonds, 2021

Navel orangeworm is the primary pest of California almonds due to its ability to cause direct damage to the salable nutmeat. We conducted 2 insecticide trials to evaluate the effects of 1 or 2-spray insecticide programs at hull split on damage at harvest. One trial was conducted during the second generation of navel orangeworm in the variety Nonpareil, while the second trial targeted the third generation in the variety Monterey. Each trial was organized as a randomized complete block design using 6 blocks of single-tree plots. There were 10 treatments, each consisted of either a single insecticide application at hull split (HS), or a 2-spray program with 1 spray at HS and another approximately 2 weeks later at post-hull split (PHS). Additionally, there was an untreated check. The trial was located in a 14-year-old research orchard, managed by the authors, at a university farm in Shafter, CA.

A gas-powered wand sprayer was used to apply the treatments at 150 PSI calibrated to deliver 200 gallons of water per acre. Applications were made in the Nonpareil trial on 6 July (HS) or 19 July (PHS), and in the Monterey trial on 28 July (HS) or 12 August (PHS). All treatments included Dyne-Amic as a surfactant at a rate of 12.8 fl oz/acre (0.0005% v/v). Nonpareil and Monterey nuts were harvested on 11 August and 15 September, respectively, by placing a tarp under each tree and using a pole to knock down approximately 500–1,000 nuts. Care was taken to collect nuts from the entire height of each tree. Nuts on the tarp were gathered, mixed, and a subsample of approximately 250–300 nuts was placed into a paper sack. Sacks of nuts were placed indoors in an ambient-temperature warehouse to dry for approximately 2 weeks, after which all samples were placed into cold storage for future processing. In November, all nuts were cracked open and the percentage of nuts infested with NOW was determined. Data from each trial were processed independently and then across varieties by ANOVA after arcsine transformation (arcsine(sqrt(x))) to normalize variances. Means were separated using Fisher’s Protected LSD (α = 0.05).

Both trials had high navel orangeworm pressure, with the Nonpareil check averaging 8.8% of nuts infested and the Monterey check averaging 26.9% (Table 1). In the Nonpareil trial, significant reductions in damage were seen in the 2-spray programs of Spear-Lep + Leprotec followed by Intrepid, and the 2-spray program with MBI-306. In the Monterey trial, significant reductions were seen in NOW damage following single applications of Intrepid, Intrepid Edge, and Altacor, and with 2-spray programs of Intrepid followed by Spear-Lep + Leprotec, and of 2 applications of MBI-306. When data were analyzed across trials, all treatments significantly reduced damage except for single applications of Spear-Lep + Leprotec and Verdepryn, and the 2-spray program with Venerate.

This research was supported in part by industry donations of pesticides and research funding, with maintenance costs for the experimental almond orchard provided primarily by the Almond Board of California.