Evaluation of Insecticides for San Jose Scale Management in Georgia Peaches, 2019

The objective of this study was to evaluate the efficacy of several insecticides and timings against San Jose scale (SJS) on Georgia peaches. Single-tree plots were established in a 9-yr-old planting of ‘Springprince’ peach trees with a row spacing of 20 ft × 18 ft; located at the Fort Valley State University research farm in Fort Valley, GA. A total of 11 treatments were evaluated and replicated four times each 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 single-nozzle boom calibrated to deliver 100 gpa at 40 psi (Table 1). Treatment applications were initiated at delayed-dormant timing on 26 Feb, shuck off on 6 Apr, and then followed a schedule based on the first and second peak activity events for the SJS immature stage, or ‘crawlers’ (Table 1). The crawlers were monitored starting on 24 Apr 2019, proceeding on a weekly basis through harvest until 23 Aug 2019 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. The number of SJS crawlers on each tape (adjusted to per 5 cm of tape) were counted using a stereomicroscope. Due to a late freeze, we were unable to assess fruit injury. The mean abundance of crawlers per 5 cm of tape at pre-harvest (24 Apr through 28 Jun 2019) and seasonal summation (24 Apr through 23 Aug 2019) were compared across the 11 treatments using ANOVA (data were natural log-transformed) and means separation with Student’s t (P < 0.05).

There were no significant treatment differences for the number of SJS crawlers per 5 cm collected during the pre-harvest period of 24 Apr to 28 Jun 2019 (F = 1.01, df = 10, 333, P = 0.461). Numerically, all the treatments had considerably fewer scale crawlers than the UTC, but due to high levels of variation and relatively low numbers of SJS crawlers early in the season, these differences were not significant (Table 1).

Evaluating the abundance of crawlers per 5 cm collected from 24 Apr through 23 Aug, there were significant differences among treatments for the total abundance of crawlers (F = 3.3, df = 9, 30, P = 0.006). Although numerically lower, by the end of the season, only three treatments—Venerate alone at delayed-dormant timing, 1.5% Omni Supreme Spray at 100 gpa, and 4% Omni Supreme Spray at 100 gpa—did not have significantly lower abundances of SJS crawlers than the UTC (Table 1). The Movento + Sivanto Prime had the lowest overall abundance of SJS at the end of the season, followed by Movento alone, 4% Omni Supreme Spray at 200 gpa, and Venerate applied at the first- and second-generation timings for SJS crawlers. These results suggest that although there is still no silver bullet for SJS management, there are several compounds that can effectively suppress SJS populations in Georgia peaches. Remarkably, though, management with 4% Omni Supreme Spray at 200 gpa during delayed-dormant timing did not statistically differ from 1.5% Omni Supreme Spray at 200 gpa or 4% Omni Supreme Spray at 100 gpa. Similarly, Movento + Sivanto Prime had the lowest overall abundance of SJS but was not statistically different than Movento alone. Nonetheless, the numerically fewer SJS crawlers throughout the season with the 4% Omni Supreme Spray at 200 gpa and the Movento + Sivanto Prime treatments may lead to fewer SJS the following season, which may result in accumulative control after years of management. This, along with the effective management with Venerate XC, provide encouraging results for new and effective SJS management tools in addition to the proven insect growth regulators.¹

Footnotes