Effect of simulated rainfall on the effectiveness of insecticides against spotted wing drosophila in blueberries

Abstract

The current spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae) management strategy relies on routine application of insecticides during the fruit ripening and harvesting period. The amount and frequency of insecticide spray needed to maintain continuous protection of fruits may depend on a variety of factors including the level of rainfall. Studies were conducted to determine the effects of simulated rainfall (0, 12.5, 25 and 37.5 mm) and adjuvant-Nu Film (with and without) on the residual efficacy of commonly used insecticides against D. suzukii in blueberries during the fruiting season of 2014 and 2015. Spray applications were made using an air-assisted backpack (2014) or airblast (2015) sprayer. Insecticide spray residues were allowed to dry for ~2 h before simulated rainfalls were applied using central pivot irrigation system. Semi-field bioassays were conducted to assess mortality at 1, 3 and 7 days after treatment (DAT). Results showed that simulated rainfall caused a significant reduction in D. suzukii mortality in all chemical treatments, particularly at 1 and 3 DAT in the 2014 study, and at 1 DAT in the 2015 study. In general, higher rainfall resulted in lower mortality in 2014, however such a clear trend was not observed in 2015. Addition of adjuvant, Nu Film 17, significantly increased mortality at 3 DAT in the zeta-cypermethrin treatment with 25 mm of simulated rainfall (2014). In 2015, the addition of Nu Film P significantly increased mortality at 1 DAT in the spinetoram and spinosad treatments with 12.5 mm, and in the malathion treatment with 25 mm of simulated rainfall. These results suggest that although frequent rainfall incidents increase the need for more frequent spray of insecticides, addition of adjuvants helps to prolong the residual efficacy of some insecticides.

Efficacy of biopesticides on spotted wing drosophila, Drosophila suzukii Matsumura in fall red raspberries

“…However, rainfall, particularly in the first week of the experiment did coincide with the poor efficacy of insecticides as seen in the consistently high infestation in fruit. The efficacy of spinosad was previously shown to be significantly reduced by simulated rainfall between 12.5 and 25 mm (Gautam et al., ). Effective insecticide treatments in this experiment significantly reduced the number of larvae in infested fruit, with some treatments reducing the number of third instar larvae of D. suzukii in fruit.…”

Evaluation of adjuvants to improve control of spotted‐wing drosophila in organic fruit production

“…In a rain fastness study, Gautam et al () observed that the effectiveness of insecticides, including spinosad, declines rapidly in the field even in the absence of rainfall. The addition of P1M did not improve residual activity (Gautam et al, ). The adjuvant PEPMS had significant effects on adult mortality with C. subtsugae and spinosad and on progeny with azadirachtin + pyrethrins and C. subtsugae .…”

“…Drosophila suzukii adults used in bioassays were taken from separate laboratory colonies established by each collaborating university. Cultures were maintained on a standard cornmeal‐molasses (or cane sugar)‐yeast medium (Gautam et al, ; Jaramillo, Mehlferber, & Moore, ). Adults used in bioassays were 4–10 days old and were not starved prior to use in bioassays.…”

“…On both conventional and organic farms, insecticide use has increased since the arrival of this pest (Diepenbrock et al, ; Van Timmeren & Isaacs, ). Three classes of pesticides show good insecticidal activity against D. suzukii : organophosphates, pyrethroids and spinosyns (Beers, Van Steenwyk, Shearer, Coates, & Grant, ; Bruck et al, ; Gautam et al, ; Van Timmeren & Isaacs, ). Organic growers have few pesticide options for control of D. suzukii compared to conventional growers, and spinosad is the most effective organically approved product for its control (Beers et al, ; Bruck et al, ; Cahenzli, Strack, & Daniel, ; Van Timmeren & Isaacs, ).…”

“…They are products commonly used and available for organic growers in the United States. Gautam et al () and Wise et al () used P1M in their experiments, but most insecticide studies targeting D. suzukii have not included adjuvants. Fanning et al () used eight adjuvants including PEPMS in their study, but they only tested these in combination with a single product.…”