Study on the effect of different adjuvants on dimethomorph against lettuce downy mildew

The influence of four adjuvants, including organosilicon surfactant Silwet 408, anionic surfactant Jiecheng, vegetable oils Coerce and WETCIT, on the effective utilization and bioactivity of dimethomorph 50% WP against lettuce downy mildew was conducted by spraying method. The deposition rates of dimethomorph without adjuvants, and with Silwet 408, Jiecheng, Coerce and WETCIT were 4.10, 5.71, 6.24, 9.18 and 7.41 mg/kg, respectively, 1 day after the first application, and the deposition rates of dimethomorph on lettuce plant were 26.35%, 36.73%, 40.08%, 59.01% and 47.63%, respectively. The field control efficacy of dimethomorph against lettuce downy mildew, 7 days after the second application, were 63.82%, 89.90%, 77.84%, 76.35% and 76.94%, respectively. The maximum deposition and deposition rates after the treatment of dimethomorph (recommended dosage reduced by 10%) with Coerce were significantly higher than those after the treatment of dimethomorph for recommended dose and without Coerce (control group). And no significant difference was found in the control effect of downy mildew. There were no significant difference between the treatment of dimethomorph (recommended dosage reduced by 20%) with Coerce and the control group. However, the treatment of dimethomorph (recommended dosage reduced by 30%) with Coerce were significantly decreased than the control group. The results indicated that all the tested spray adjuvants showed certain synergistic effect on dimethomorph. Vegetable oils had strongest effect on increasing the deposition rate of dimethomorph, while organosilicon surfactants had strongest effect on improving the bioactivity of dimethomorph against lettuce downy mildew. While ensure the effective utilization and control effect, adding a certain concentration of spray adjuvant can reduce the use of pesticides by 10%-20%.