Increasing Cyetpyrafen Spray Volume and Ozone Spray Improves the Control Effects against Two-Spotted Spider Mite (Tetranychus urticae) in Strawberries

Abstract

The two-spotted spider mite (Tetranychus urticae) is a constant threat to greenhouse strawberry production. The application of synthetic acaricides is the main method of controlling T. urticae. However, resistance development to traditional acaricides reduces their efficacy and eventually leads to control failure. It is important for strawberry growers to look for new acaricides and application technologies that can limit the harmfulness of T. urticae in environmentally friendly ways. In the current study, laboratory toxicity tests and field trials were performed to screen high-efficiency acaricides, and then application technologies were improved to enhance the management of T. urticae. In the laboratory toxicity tests, the results showed that the LC₅₀ (median lethal concentration) value of cyetpyrafen, cyenopyrafen, cyflumetofen, bifenazate, abamectin, azocyclotin, pyridaben, spirodiclofen, and etoxazole against adult T. urticae was 0.226, 0.240, 0.415, 3.583, 5.531, 25.58, 39.69, 140.3, and 267.7 mg/L, respectively. In addition, the LC₅₀ value of the nine acaricides against eggs of T. urticae was 0.082, 0.097, 0.931, 18.56, 25.52, 45.61, 36.32, 1.954, and 0.040 mg/L, respectively. The field trial results showed that the best control effect was obtained in cyetpyrafen at 300 mL/ha treatment. Cyetpyrafen was chosen for further application technology tests. In the spray volume tests, the results showed that increasing the spray volume from 900 to 1050 L/ha significantly improved the control of T. urticae. In addition, the results from the spray instrument tests demonstrated that the control effects on T. urticae in the ozone spray treatments were significantly higher than those of the conventional and electrostatic sprays 1 and 3 days after treatment (DAT). Therefore, this study suggested that cyetpyrafen effectively controlled T. urticae both in the laboratory tests and in the field trials. Increasing the spray volume and application of ozone spray significantly improved T. urticae management.

Keywords: Tetranychus urticae; cyenopyrafen; ozone spray.

Figure 1

Control effect of acaricides on Tetranychus urticae in field trials one day after treatment. Control effect (%) = (the decrease rate in the control mite population − the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).

Figure 2

Control effect of acaricides on Tetranychus urticae in field trials three days after treatment. Control effect (%) = (the decrease rate in the control mite population − the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).

Figure 3

Control effect of acaricides on Tetranychus urticae in field trials seven days after treatment. Control effect (%) = (the decrease rate in the control mite population− the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).

Figure 4

Control effect of acaricides on Tetranychus urticae in field trials fourteen days after treatment. Control effect (%) = (the decrease rate in the control mite population − the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).

Figure 5

Control effect of different spray volumes on Tetranychus urticae in field trials. Control effect (%) = (the decrease rate in the control mite population − the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).

Figure 6

Control effect of the spray instrument on Tetranychus urticae in field trials. Control effect (%) = (the decrease rate in the control mite population − the decrease rate in the treated mite population)/(100 − the decrease rate in the control mite population) × 100. The data are represented as the mean ± standard deviation of the mean and separated with Tukey’s HSD test. The same letters above the columns indicate that the values are not statistically different (p < 0.05).