The influence on wettability, retention of sulfoxaflor at Fuji apple leaves surface by adding spray adjuvants

In order to clarify the important role of spray adjuvants in the chemical control of apple orchard, the effects of three spray adjuvants GY-T12, NF-100 and Mairun on the physicochemical properties, wettability and retention of sulfoxaflor 22% SC were evaluated at CMC by measuring the surface tension, the contact angle and the maximum retention, and the synergistic effects to Aphis citricola were investigated. The results showed that the addition of three spray adjuvants reduce the surface tension of solutions from 50.65 mN/m to 27.64-35.64 mN/m. According to the contact angle of water droplets on the surface of apple leaves, less or greater than 90°, the adaxial surface is judged as a hydrophilic surface and the abaxial surface was judged as a hydrophobic surface. The addition of adjuvants decreases 30 seconds static contact angles on the adaxial surface by 23.2°-41.3° and by 68.0°-93.5° on the abaxial surface. The wettability assay showed when the concentrations of three spray adjuvants reached CMC, the adhesion work decreased by 5.36-12.56 mJ/m² while the adhesion tension increased by 9.27-11.26 mN/m between the droplets and the adaxial surface, the adhesion work and adhesion tension increased by 27.45-36.66 mJ/m² and 47.55-53.28 mN/m between the droplets and the abaxial surface. Then, the regression equation between the maximum retention and surface tension was established, it showed that the maximum retention is 12.53 mg/cm² when the surface tension is 40.89 mN/m. Among the three spray adjuvants, NF-100 and GY-T12 significantly increase the retention of pesticides, moreover, the synergistic effect of GY-T12 on A. citricola is notable. Therefore, the selection of spray adjuvants in apple orchards should macth the expected goals, and the proper adjuvant is feasible to regulate the surface tension of pesticide in an appropriate range to increase the retention and improve the toxicity to target pests.