Comparing the Efficacy of Entrust SC Mixed With and Without a Novel Adjuvant, Combi-Protec, Against Spotted-Wing Drosophila in Blueberries, 2021

A semi-field bioassay was conducted to assess the efficacy of Entrust 2SC Naturalyte (spinosad) when mixed with a novel adjuvant, combi-protec, for managing spotted-wing drosophila (SWD) in rabbiteye blueberries. This experiment was conducted at Blueberry Research and Demonstration Farm in Alma, GA (31.5346, −82.5099). The field was planted with rabbiteye blueberry varieties ‘Brightwell’, ‘Climax’, and ‘Powderblue’ recurring every third row. Plants are spaced at 1.5 m between plants and 3.7 m between rows. This bioassay included eight treatments, including Entrust 2SC, mixed with and without the adjuvant combi-protec, treated to blueberry fruits alone, plant terminals alone, or both, a treated check of combi-protec spray, and an untreated check (Table 1). Individual plots consisted of three blueberry plants of the ‘Powderblue’ variety. The plots received treatments on 30 Jun. Treatments were carried out using a CO₂-pressurized backpack sprayer fitted with a spray boom with four TeeJet (TP8002-VS VisiFlo, TeeJet Technologies LLC, Wheaton, IL) flat spray tips spaced 0.48 m apart. Insecticides were applied at the highest field recommended rate at 40 psi and a carrier volume of 467.7 liters/ha. The adjuvant, combi-protec, when present in treatments, was mixed with the spray solution at a rate of 1.02 liters/ha (Table 1). Plant terminals and fruits from the treated plots were collected and transported to the laboratory to conduct the bioassay. The bioassay arena consisted of a 946-ml clear plastic container (Fabri-Kal, Kalamazoo, MI) with a matching lid and with a single 5–7 cm long blueberry terminal with five leaves inserted into a floral tube filled with distilled water, which was then fitted through a circular hole in the bottom center of the arena. Each assay container was supplied with 10 ripe blueberries from the experiment plot. Bioassay containers were then arranged in an RCBD design, and treatments were replicated five times. Five male and five female adult SWD of 5–7 d old, reared from laboratory colony, were then released into individual bioassay arenas. After the flies were released, the containers were kept in a laboratory maintained at 22°C,14:10 (L:D) h, and 86 ± 10% RH for 6 d. On the 6 DAT, blueberries were removed from the bioassay containers and transferred to a ventilated 59-ml clear plastic souffle cup (Fabri-Kal, Kalamazoo, MI) with a cotton round (Swisspers, Gastonia, NC) in the bottom, and incubated in a growth chamber (Percival Scientific, Inc., Perry, IA), at 24°C,14:10 (L:D) h, and 60 ± 2% RH for 6 d.

Treatment efficacy was determined based on the adult SWD mortality in the bioassay chambers containing treatments and the number of SWD larval progenies present in the blueberry fruits. The experiment was initiated on 30 Jun, and posttreatment male and female SWD mortality counts were taken on 1 Jul, 3 Jul, and 6 Jul (1, 3, and 6 DAT, respectively). Additionally, larval progeny counts from blueberries were taken on 12 Jul (12 DAT). Larval progeny counts from the incubated blueberries were taken using the filter salt extraction method. Data were subjected to ANOVA (PROC GLIMMIX, SAS v. 9.4) with data fitted to a normal distribution, and the mean (LSMEAN option) separation was carried out using the Tukey–Kramer method (P ≤ 0.05). Larval progeny count data were square-root transformed (sqrt + 1) before analysis, and untransformed means were reported.

There was a significant difference in adult SWD mortality among the treatments at 1, 3, and 6 DAT (Table 1). At 1 DAT, compared with the untreated check, significantly higher SWD mortality was observed in the arena where both plant terminal and blueberries were treated with Entrust + combi-protec solution. Additionally, at 3 and 6 DAT, all the insecticide treatments mixed with combi-protec resulted in significantly higher SWD mortality than the untreated check. Moreover, compared with the untreated check, significantly fewer larval progenies were recovered from treatments in which the blueberry fruits received Entrust 2SC application with or without added combi-protec.¹

Footnotes