Control of Spotted Wing Drosophila in Highbush Blueberries, 2016

The objective of this experiment was to test the efficacy of multiple applications of Delegate WG and Imidan 70WP against spotted wing drosophila (SWD) in a mid-season highbush blueberry var. ‘Bluecrop’ in New Jersey. The insecticide treatment rates were Delegate WG at 6 oz/acre and Imidan 70WP at 1.33 lb/acre (grower standard), applied weekly during harvest on 14 Jul, 21 Jul, and 26 Jul 2016. The experiment was conducted in an abandoned blueberry farm located in Pemberton, New Jersey. Plots consisted of two rows of approximately 15–20 bushes each, replicated four times in a CRB design. Control plots received no insecticides. Treatment rows were separated by single buffer rows, and treated plots were separated by 2–3 bush buffer zones. Applications were made with a Pak-Blast model MBICO28 Plot Sprayer (Rear’s Mfg Co., Eugene, Oregon) on a John Deere 5320N Tractor. The sprayer was calibrated to deliver 40 gal of vol per acre at 200 psi using four nozzles with D3 orifices, yielding approximately 125.12 ml (4.23 fl oz) per bush.

Treated terminals with 3–4 leaves were taken twice (on 14 and 26 July) from each treated bush, along with 10 ripe blueberries. After the first week application (14 Jul), samples were taken 1, 3, and 7 DAT on 15 Jul, 17 Jul, and 21 Jul. After the third week application (26 Jul), samples were taken 0, 3, and 6 DAT on 26 Jul, 29 Jul, and 1 Aug, respectively. Terminals were placed in assay containers consisting of 32-oz deli cups with a hole in the bottom where a florist’s water pick fitted tightly. Terminals were supplied with water and kept in a laboratory (14:10 [L:D] h photoperiod, ~20–28°C) during the length of the experiment. Ten berries, obtained from the corresponding treated plots, were placed in the bottom of each assay container before flies were added. Flies were added to the assay containers within 3–4 h after terminals were clipped from bushes. For each assay, a total of 10 adult flies (five females and five males) were removed from a SWD colony and released into each assay container. Flies were 4–6 days old at the time of use, so they were assumed to be sexually mature. Flies were anesthetized with small puffs of CO₂ injected into the rearing tubes to facilitate handling and placement in the assay containers. Data on adult mortality were collected at 24 and 48 h after exposure to the treated fruit and foliage, and percent live, moribund, and dead were calculated. An additional 5–7 days were allowed for continued oviposition by female flies. Berries were then removed from assay containers on day 7, placed in 8-oz deli containers, and incubated under the same conditions for 10 additional days before evaluation. Larval infestation data were collected using a salt water extraction method consisting of submerging the berries in warm salt water (~1000-ml NaCl: 5-gal H₂O) which causes the larvae to exit the fruit. Larvae and pupae caught by a 30-mesh sieve were counted and the number of larvae per berry was calculated (no. of larvae/no. of ripe fruit, ‘larvae’ includes all larvae + pupae). Data were analyzed using ANOVA and means separation by Tukey’s LSD test at α = 0.05. Percent mortality data were arcsine square-root transformed and larval count data were ln(x+0.1)-transformed prior to analysis. Percent controls were calculated for both adults and larvae. Percent adult control was calculated using the following formula: [1 − (no. live flies in treatment/no. live flies in control)] × 100. Percent larval control was calculated using the following formula: [1 − (no. larvae in treatment/no. larvae in control)] × 100.

Both Delegate and Imidan provided good control against SWD 0–1 DAT (Tables 1 and 2). On the first week of evaluation, adult mortality and larval infestation was >95% for both Delegate and Imidan treatments at 1 DAT (Table 1). However, the toxicity effects of Delegate, but not Imidan, declined at 3 and 7 DAT. On the third week of evaluation, adult mortality and larval infestation was >90% for both Delegate and Imidan treatments at 0 DAT (Table 2). But this time, the efficacy of Delegate remained high (80–100%) and similar to Imidan (100%) at 3 and 7 DAT. No phytoxicity symptoms were observed following any of the insecticide treatments.

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