Evaluation of Insecticides for San Jose Scale Management in Georgia Peaches, 2017 Open Access

The objective of this study was to evaluate the efficacy of several insecticide rates and timings against SJS on Georgia peaches. Single-tree plots were established in an 8-yr-old planting of ‘Juneprince’ peach trees with row spacing of 20′ × 18′, located at the Fort Valley State University research farm in Fort Valley, GA. Treatments were replicated four times in an RCB design with at least one buffer tree separating all plots. All treatments were applied using a backpack CO₂ sprayer (Bellspray, Inc.) with a two-nozzle boom calibrated to deliver 100 gpa at 40 psi (Table 1). The immature stage of SJS, or ‘crawlers,’ was monitored starting on 27 Mar 2017, proceeding on a weekly basis through harvest until 17 Aug 2017 with a piece of double-sided tape positioned over a strip of black electrical tape and wrapped around an infested branch. Two monitoring tapes were deployed per sampling tree, and were removed and replaced on a weekly basis, and the number of SJS crawlers on each tape (adjusted to per 5cm of tape) was counted using a stereomicroscope. Additionally, 20 fruits were harvested from each of the single-tree plots on 9 Jun 2017 and examined individually for injury due to SJS (number of individual scales). The mean abundance of crawlers per 5 cm of tape at harvest, 10 days after the last insecticide application (week 33), seasonal summation, and the number of settled scale per peach at harvest were compared across the 10 treatments using ANOVA (data were log(x + 1)) transformed and means separation with Student’s t-test (P < 0.05).

There were significant treatment differences for the number of SJS per peach at harvest (F = 2.1, df = 9, 30, P = 0.041) where all treatments trees, except Venerate applied once per generation, had fewer SJS than the UTC, but there was no significant separation between the chemical treatments (Table 1). A harvest, chemically treated treatments had significantly fewer crawlers per 5 cm of tape than the UTC (F = 8.59, df = 9, 30, P = 0.0004; Table 1). By Aug 2017, the treatment differences in SJS crawler abundance were not statistically significant (F = 1.12, df = 9, 30, P = 0.376) with only the Movento, Centaur, Grandevo (twice per generation), and Venerate (twice per generation) treatments having significantly fewer crawlers than the UTC trees (Table 1). Evaluating the total abundance of crawlers per 5 cm collected from 27 Mar through 17 Aug, there were significant differences among treatments for the total abundance of crawlers per 5 cm of tape (F = 8.95, df = 9, 30, P = 0.006). Although there was marginal or no differences between the treatments and the UTC throughout the season, by the end of the season, all treatments had fewer SJS than the UTC with Centaur, Sivanto-only, and the Sivanto + Movento treatments having significantly fewer crawlers than the oil-only and the other chemical treatments (Table 1). Lower abundances of SJS crawlers at the end of the season is expected to lead to lower populations the following season, increasing the benefit of compounds as SJS management tools.

This research was supported by industry gifts of material and/or research funding.