Abstract: 【Objective】The objective of this study is to analyze the relationship between the spray volume in rice fields and retention on rice plants, understand the mechanism affecting the control effect of pesticide unit dose, and to provide a basis for the scientific use of pesticides. 【Method】 the liquid retention on unit area of ??rice was measured under spraying conditions, the change of the liquid retention indicated the point of run-off and maximum retention of the liquid on rice leaves. The surface tension of the liquid was measured by the method according to the GB/T 5549-2010, and the critical micelle concentration of the surfactant solution was determined by using the law of the surface tension varying with the concentration of the surfactant. The zisman method was used to measure the critical surface tension of rice leaves. The key factors affecting the leaf capacity of rice leaves were analyzed. By simulating chlorantraniliprole control of rice leaf roller(Cnaphalocrocis medinalis), pymetrozine and chlorpyrifos control of brown planthopper (Nilaparvata lugens) in a spray tower, the relationship between spray volume and droplet density and the effect of pesticide unit dosage on control effect against pests were also investigated. 【Result】 With the increase of the spray volume, the liquid holding capacity of rice leaves increased. After reaching the maximum value, the liquid began to lose and then it decreased to a stable value and no longer changed. The final liquid holding capacity was only 50% of the maximum value. The critical surface tension of the tested rice leaves was 29.90-31.22 mN·m^-1, which meant the tested surface was a low-energy surface. The surface tension of clear water was 71.8 mN·m^-1, which was greater than the critical surface tension of the tested surface. The surface tension of tested rice leaves limited the liquid holding capacity of the leaves. With the additives TX-10 and Silwet-408, the surface tension of the liquid was less than the critical surface tension of rice, which increased the liquid holding capacity of the rice leaves. When the auxiliary agent reached the critical micelle concentration, TX-10 and Silwet-408 provided the best results. The amount of liquid spray affected the density of spray droplets, thus affecting the control effect of pesticide unit dose. When the droplet volume median diameter was 200 μm, the amount of liquid medicine 150 L·hm^-2 was less than 10 drops/cm². The control effect of three effective doses 20, 25 and 30 g of chlorantraniliprole against C. medinalis was less than 60%. The liquid droplet volume 450 L·hm^-2 had less than 40 drops/cm². The control effect of three effective doses against C. medinalis was 56.92%, 62.86% and 65.07%, respectively. The liquid droplet volume 900 L·hm^-2 was 82 drops/cm², the three effective doses of chlorantraniliprole had the best control effect on C. medinalis, which was over 70%. Reducing the droplet volume median diameter and increasing the amount of droplets of unit volume of liquid could reduce the amount of liquid spray. When the diameter of droplets was 75 μm and the liquid volume was 450 L·hm^-2, the droplets were 140 drops/cm² and the control effect of chlorantraniliprole against C. medinalis had no significant difference with 200 μm droplet diameter and 900 L·hm^-2 liquid volume. Because of the barrier of rice canopy, the droplets number under the canopy was very few when spraying on the longitudinal surface of rice. When the droplet volume median diameter was 200 μm and the spray liquid volume was 900 L·hm^-2 or the droplet volume median diameter was 75 μm and the spray liquid volume was 450 L·hm^-2, the amount of droplets under the canopy were less than 20 drops/cm², the pesticides had poor control effect on the N. lugens. Under the canopy spray, pesticides were sprayed directly on the infestation sites of the N. lugens, and the control effect of the pymetrozine and chlorpyrifos unit doses on the N. lugens was significantly improved. 【Conclusion】 The amount of liquid used affects the amount of pesticides deposited on rice plants and the density of droplets per unit area of rice, thus affecting the control effect of pesticide unit doses on pests. When the liquid volume was 450 L·hm^-2 (droplet diameter 75 μm) or 900 L·hm^-2 (droplet diameter 200 μm), the canopy was evenly sprayed up and down in rice fields, which ensured that the liquid retention on rice plant was within the range of the point of run-off and had a sufficient density of droplets, the control effect of pesticide against pests was good.

Key words: pesticide, spraying volume, point of run-off, retention, droplet density, control effect