Evaluation of a new insecticide for controlling spotted-wing drosophila in highbush blueberries, 2023

The objective of this study was to determine the efficacy of PLINAZOLIN technology 400SC (isocycloseram) and Imidan 70WP (phosmet), used as the grower standard, for controlling spotted-wing drosophila in highbush blueberries (variety ‘Bluecrop’) in New Jersey. The study was conducted at the Rutgers P.E. Marucci Center in Chatsworth, New Jersey, with each treatment applied to 5 bushes in a CRB design. Plots were separated within a row by a 2-bush buffer and between rows by a buffer row. Applications were made with an R&D CO₂ backpack sprayer, using 2-liter plastic bottles. The sprayer was calibrated to deliver 40 gal of vol per acre at 30 psi, using a single ConeJet TXVS 10 nozzle, yielding 125.1 ml (4.23 fl oz) per bush. Treatments were as follows: 2 rates of PLINAZOLIN technology 400SC, applied at 1.54 fl oz/acre and 2.05 fl oz/acre, and Imidan 70WP at 1.33 lb/acre. All PLINAZOLIN technology treatments included the adjuvant Dynamic at 0.125% v:v. Treatments were applied on 30 Jun 2023. Control bushes received no insecticide. Total rainfall during the trial period was 0.34 inches (0.86 cm). Terminals (stems with 4–5 leaves) were taken from each bush, along with 15 ripe blueberries, within 5 h of treatment on 30 Jun (0 DAT), and again 3 (3 Jul) and 7 (7 Jul) days after treatment (3 DAT and 7 DAT, respectively). In the laboratory, the terminals were placed in florist’s water picks with an opened bottom. The tops of terminals containing the leaves were enclosed in assay containers consisting of a ventilated 32-oz plastic deli cup with a hole cut in the bottom; the florist’s water pick was fit tightly through the hole. The cut ends of terminals inside the water picks were placed in water-filled trays. Additionally, a 2-cm piece of moistened dental wick was added to each container to supply water for the flies. Five containers (replicates) were set up for each treatment on each sample date, with samples from each container coming from a single bush (N = 5 per treatment per sampling date). Fifteen loose ripe berries (obtained from the corresponding treated bush) were placed in the bottom of each container before flies were added. Flies were obtained from a laboratory colony and were added to the containers within 2 h after terminals were clipped from the bushes. For each assay, a total of 10 adult flies (5 females and 5 males) were removed from the colony and released into each container. Flies were 5–7 days old and were thus considered sexually mature. Flies were anesthetized with small puffs of CO₂ gas injected into the rearing tubes to facilitate handling and placement in the containers. After flies were added to the containers, the containers were placed on a light bench in the laboratory under a 14L:10D photoperiod and were kept at ambient temperature (~25 °C) during the observation period. Adult mortality data were collected at 1 and 3 days after exposure to the treated fruit and foliage. The number of live, moribund, and dead males and females was recorded, and their percentage was calculated. Percent control was calculated using the formula: [1 − (% live adults in treatment/ % live adults in control)] × 100. Berries were removed from the containers on day 3, and the number of eggs in each berry was counted. Following, berries were placed in ventilated 8-oz deli containers with cotton pads, incubated under the same environmental conditions as described above for 15 more days, and monitored for larval emergence and pupation. The total number of pupae from the berries was counted. Percent immature mortality was calculated using the formula: [1 − (number of pupae/number of eggs)] × 100. Data were analyzed using ANOVA with means separation by Fisher tests at P = 0.05. Percent adult mortality data were arcsine square-root transformed, and pupae count data were ln(x + 0.1) transformed prior to analysis.

At 0 DAT, PLINAZOLIN technology significantly increased adult mortality but by <80% after 3 days of exposure; in comparison, Imidan provided 100% mortality (Table 1). Even though mortality was not as high, PLINAZOLIN technology reduced the number of eggs laid at 0 DAT to levels comparable to Imidan (Table 1). At 3 DAT, adult mortality by PLINAZOLIN technology was <70% after 3 days of exposure, while mortality by Imidan remained high (100%) (Table 2). The number of eggs laid at 3 DAT was significantly reduced by PLINAZOLIN technology and Imidan compared to the control (Table 2). At 7 DAT, adult mortality by PLINAZOLIN technology was low (<20%) after 3 days of exposure, while mortality by Imidan continued to be high (90%) (Table 3). Compared to the control, the number of eggs laid at 7 DAT was significantly reduced by PLINAZOLIN technology at the high rate, but not to the levels reduced by Imidan (Table 3). Based on pupal counts, both PLINAZOLIN technology and Imidan significantly reduced the survival of immatures in berries even at 7 DAT (Table 4). No phytotoxicity symptoms were observed following any of the insecticide treatments.¹

Footnotes