Spread and evaporation characteristics of droplets with surfactant on Eucalyptus leaves

Abstract. Surfactant had effect on the spread and evaporation characteristics of spray solution. Dimethyl Dichloroviny Phosphate (DDVP), Efficient Cypermethrin (EC) and deionized water were tested for comparison. DDVP and EC were diluted 1000 times with deionized water respectively. Three solutions were added with and without 0.1%, 0.25%, 0.5%, 1% surfactant concentrations (SCs) of 2201 nonionic surface surfactant respectively. The contact characteristics of 500µm and 250µm droplets at different positions on Eucalyptus Tereticornis (ET) leaves were measured under the 30ºC temperature and 60% relative humidity (RH). The positions included the interveinal area, midrib and secondary vein on the adaxial and abaxial surfaces. Droplets without surfactant didn't spread and had the longest evaporation time. With surfactant, for deionized water droplets, the wetted area increased and evaporation time decreased promptly at 0.1% SC. With the SC increasing, both of the values presented decreasing trend and reached the minimum at 1% SC. 0.1% was the ideal SC for Deionized water. For DDVP and EC, the wetted area increased but evaporation time decreased with the SC increasing. Droplets could attain the relative larger wetted arae and longer evaporation time at 0.25% SC. 250µm droplets had better spread effectiveness than 500µm droplets. Droplets on the adaxial surface had greater wetted area but shorter evaporation time than those on the abaxial surface. It took droplets most of the time to spread but little time to penetrate after deposition. During the application of pesticides, small droplets and proper SC should be considered to improve the use efficiency of pesticides.