Efficacy of new insecticides against plum curculio in highbush blueberries, 2023

This experiment tested the efficacy of PLINAZOLIN technology 400SC (isocycloseram), Verdepryn 100SL (cyclaniliprole), and Imidan 70WP (phosmet) (used as the grower standard) against plum curculio in highbush blueberries. All PLINAZOLIN technology treatments included 0.125% v/v of the non-ionic surfactant Dynamic. The experiment was conducted in a highbush blueberry field (variety ‘Duke’) located at the Rutgers P.E. Marucci Center in Chatsworth, New Jersey. Each treatment was repeated on 5 individual bushes in a CRB design, with each bush considered a replicate (total of 7 treatments × 5 plots = 35 bushes). Plots (n = 5) of 7 bushes each (blocks) were separated within rows by a 2-bush buffer zone and between rows by a buffer row. Treatments were PLINAZOLIN technology 400SC at 1.03, 1.54, and 2.05 fl oz/acre (+ 0.125% Dynamic), Verdepryn 100SL at 8.2 and 11 fl oz/acre, and Imidan 70WP at 1.33 lb/acre. Control bushes received no insecticide. Applications were made on 21 May 2023 with an R&D CO₂ backpack sprayer, using 2-L plastic bottles. The sprayer was calibrated to deliver 40 gal of volume per acre at 30 psi, using a single ConeJet TXVS 10 nozzle, yielding 125.1 ml (4.23 fl oz) per bush. No rainfall occurred during the trial. After application, a single leaf terminal and 30 green berries were randomly selected from the upper two-thirds of each bush within a treatment block approximately 12 h after treatment (0 DAT) and again at 3 DAT and 5 DAT. Leaf terminals contained approximately 4–5 leaves. Berries were sampled individually and inspected before use in the assay to remove any injured or pre-infested fruit. Leaf terminals were placed in florist’s water picks with an opened bottom. The tops of the terminals containing the leaves were enclosed in assay containers consisting of a ventilated 32-oz plastic deli cup (PrimeSource, Chattanooga, TN) with a hole cut in the bottom; the florist’s water pick was fit tightly through the hole. The cut ends of the terminals inside the water picks were placed in water-filled trays. Five containers were set up for each treatment on each sample date, with the terminal and berries in each container coming from a different bush (replicate). Fifteen undamaged green berries (obtained from the corresponding treated bushes) were placed loosely in the bottom of each container before plum curculio adults were added. Adults used in the experiment were collected from unsprayed plots from 2 commercial blueberry farms located in Hammonton, New Jersey, using beating sheets from 10 to 19 May. The field-collected adults (approximately 800) were placed in ventilated 32-oz deli containers and were kept in an incubator at 15 °C and 14 L:10 D cycle and were provided with fresh, untreated blueberry foliage (no berries) and moist cotton balls every 2–3 days. On 20 May (2 days before being used in the assay), adults were moved to a light bench in the laboratory (23 °C and 14 L:10 D cycle). All adults were checked for vitality on 22 May before being placed in assay containers. The containers also had a water source for the adults consisting of a 75-mm plastic test tube filled with distilled water with a dental wick inserted at the top. Assay containers were placed on a light bench in the laboratory under a 14 L:10 D photoperiod and were kept at ambient temperature (~23 °C) during the observation period. On 22 May (0 DAT), 5 field-collected plum curculio adults were added to each container, approximately 12 h after treatment application. This sampling and assay setup was repeated on 24 May (3 DAT) and 26 May (5 DAT). The number of adults alive, moribund, or dead was assessed at 24, 72, and 120 h after exposure to treated foliage and fruit. After the last adult evaluation (120 h after exposure), all berries were removed from assay containers and evaluated for oviposition scars. Berries were then placed in ventilated 8-oz deli cups on cotton pads and incubated on a laboratory bench (23 °C and 14 L:10 D cycle) for 20 days before being evaluated for the presence of emerged larvae. To evaluate infestation, berries were dissected under a magnifying scope to determine the presence and status of any larvae within them. The total number of fruits, number of scarred fruits, and number of emerged larvae were recorded. Percent data were arcsine square-root transformed prior to analysis. Larval count data were ln(x + 0.01)-transformed prior to analysis. Data were analyzed using ANOVA and means separation by Fisher’s LSD test at P ≤ 0.05.

All insecticides (PLINAZOLIN technology, Verdepryn, and Imidan) increased adult mortality at 0 DAT (Table 1); however, compared to PLINAZOLIN technology and Imidan, Verdepryn had a slower acting effect, achieving high mortality only 5 days after exposure (Table 1). At 3 DAT (Table 2) and 5 DAT (Table 3), PLINAZOLIN technology and Imidan continued to have a strong effect on adult mortality (95–100%), while the residual effect of Verdepryn on adult mortality decreased. Imidan, PLINAZOLIN technology, and Verdepryn significantly reduced the percent of scarred fruits and the number of emerged larvae (Table 4).¹

Footnotes