Correlation Study Between High Efficiency Use Of Pesticide And Spray Method,Droplet Density

The wetting behavior and dynamic analysis of48%chlorpyrifos EC and25%pymetrozine WP before and after adding surfactant on adaxially and abaxially leaf of Nanjing11and Nanjing44were researched at different growth stages in this paper. Then, the correlation between the droplet density、spray method and the control efficiency against the brown planthopper, Nilaparvata lugens, was investigated by the spray tower. On this basis, the influence of spray method on droplet density, deposition of space of rice and efficiency against rice planthopper were discussed on field using knapsack mist blower. The main results were as follows.1. According to the continuing study of different growth stages of Nanjing11and Nanjing44, we found that the critical surface tension was30.79-32.48mN/m. The order of the critical surface tension at different growth stages was Tillering stage> Flowering stage> Filling stage. The order of the critical surface tension of different rice leaves was abaxially leaf>adaxially leaf. The order of the critical surface tension at different varieties was Nanjing44>Nanjing11. The behavioral characteristic of different surface tension of48%chlorpyrifos EC and25%pymetrozine WP before and after adding surfactant was studied, the results showed that only when the surface tension of the solution was less than the critical surface tension of the leaves, at the same time, the concentration of the surfactant reached liquids critical micelle concentration, can the solution wetting and spreading on surface of crop plant.2. The influence of the droplet densities and spray methods on the control efficiency of48%chlorpyrifos EC and25%pymetrozine WP against the brown planthopper, Nilaparvata lugens, was investigated by the spray tower of3WP-2000choosing cone nozzle and fan nozzle TP6501E. The results showed that the control efficacy might attain80%when the densities reached99.4particle/cm2and94.9particle/cm2, respectively, while the effective dose of48%chlorpyrifos EC were above68.00mg/m2and55.64mg/m2, respectively when spray downwards. The efficacy all exceeded80%when the droplet densities were10.4-49.0particle/cm2and12.3-55.4particle/cm2, respectively, and the effective dose of48%chlorpyrifos EC were41.21-82.42mg/m2and72.12-82.42mg/m2. respectively when spray laterally. The control efficacy might attain75%when the densities both reached110.5particle/cm2, respectively, while the effective dose of25%pymetrozine WP were above10.61mg/m2and9.85mg/m2, respectively when spray downwards. The efficacy all exceeded75%when the droplet densities were33.7-62.4particle/cm2and14.2-56.4 particle/cm2, respectively, and the effective dose of25%pymetrozine WP were7.58-10.09mg/m2and6.32-10.09mg/m2, respectively when spray laterally. The control efficacy of spraying laterally was significant higher than that of spraying downwards with the same effective dose. The base of rice can easily get high droplet density to ensure satisfactory efficiency at low dose when spray laterally.3. Sparging25%pymetrozine WP to control rice planthopper using knapsack mist blower for field trials, the methods of the downdip spray、drifting spray and lateral spray were used. We collected droplets by water sensitive paper, analysed droplets density and coverage by common image processing software, collected the deposition of Ponceau2R by microslide, determined the deposition of pymetrozine per unit area using the standard curve method. The results indicated that the upper droplets density and coverage> the middle density and coverage>the bottom droplets density and coverage at the same angle when downdip spray and drifting spray; the bottom droplets density and coverage>the middle density and coverage> the upper droplets density and coverage when lateral spray. The bottom droplets density of lateral spray was significantly higher than that of downdip spray and drifting spray; the middle droplets density of downdip spray and lateral spray was higher than that of drifting spray.4.The upper deposition>the middle deposition> the bottom deposition when downdip spray and drifting spray, the bottom deposition>the middle deposition>the upper deposition when lateral spray. The bottom deposition of lateral spray was significantly higher than that of downdip spray and drifting spray; the middle deposition of downdip spray and lateral spray was higher than that of drifting spray. With the increasing of volume, the total deposition of25%pymetrozine WP on each sample point increased when downdip spray and drifting spray, however, the total deposition decreased when lateral spray. The total deposition of25%pymetrozine WP on each sample point was13-25ug when downdip spray at different volume, while, the total deposition was5-12ug when drifting spray and lateral spray.5. After1day of field treatment, the control efficiency of downdip spray was46.99%-56.53%, the control efficiency of lateral spray was50.05%-72.77%, which was significantly-higher than that of drifting spray. After5days of field treatment, the control efficiency of downdip spray was67.48%-82.43%, the control efficiency of lateral spray was67.82%-77.54%, which was also significantly higher than that of drifting spray. It demonstrated that the control efficiency of pesticide was related to middle-bottom droplet density and deposition. After23days of field treatment, the control efficiency all exceeded90%. There was no significant difference between treatments. On one hand, pymetrozine had strong systemic and conductivity, on the other hand the rice planthopper migrated due to natural cause, influenced the accuracy.