Control of Spotted Wing Drosophila in Jersey Blueberry, 2020 Open Access

This trial evaluated the efficacy of insecticide programs against Spotted Wing Drosophila (SWD) in blueberry. Programs included two to five applications of one or more insecticides used in rotation over a 5-wk period. Two-bush plots were established in a mature ‘Jersey’ blueberry planting (4 × 12 ft spacing) at the Nye farm, located approximately 3 miles southwest of Trevor Nichols Research Center in Fennville, MI. Treatment plots were replicated four times and set up in an RCB design. Applications began 22 Jul at first adult SWD trap catch with ripe fruit and were re-applied at weekly intervals over the next 4 wk. Test materials were applied with an FMC 1029 airblast sprayer calibrated to deliver 50 GPA at 2.5 mph. No foliar maintenance pesticides were applied to the test plots during the trial.

Fruits were hand-harvested on 28 Jul and 4, 11, 18, 25 Aug, approximately 6 d after each application. A one-pound sample of blueberries was collected from each plot and weighed using an analog scale. Plots containing less than one pound of fruit at a sample date received a calculated value of SWD per pound. The fruit samples were evaluated through the Washington State Department of Agriculture brown sugar method as follows. Blueberries were crushed in a sugar solution containing 7 pounds of brown sugar to 5 gallons of water. The SWD larvae were allowed to float and were subsequently counted. Data of the number of larvae per pound of fruit were square-root transformed and then analyzed using ANOVA with means separated by Tukey’s HSD at P = 0.05.

Based on the 28 Jul fruit evaluation, we suspect that some fruit were already infested before the 22 Jul application (Table 1). At the 11 Aug evaluation, the incidence of SWD was significantly reduced in plots that had received three applications of Mustang Maxx, three applications of a tank mix of Bifenture and Assail, or a rotation of the low rate of Spear-T followed by Mustang Maxx and then back to the low rate of Spear-T. Rotations including the medium and high rate of Spear-T were not significantly different from the untreated check and were statistically equivalent to the rotations, including the lower use rate. On 19 Aug, all treatments except Pyrifluquinazon significantly reduced the incidence of SWD compared to the untreated check. In the final evaluation on 25 Aug, the only program to cause significant reductions in SWD was the program including five applications of a tank mix of Bifenture and Assail.¹

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