Drop Formation and Impaction on the Plant

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Abstract
The effect of variables that influence the retention of spray droplets impacting on leaf surfaces was studied, using a uniform-size droplet generator to produce drops ranging from 63 to 545 μm diam. To observe the impaction of spray droplets more easily and to measure their velocity before and after impaction, high-speed motion photography (6000 frames/sec) was used. Rebound of spray droplets depends on the micro-structure of the target surface. Leaf surfaces of several crops and weeds reflected 63 to 545 μm diam water drops traveling at velocities less than velocities of drops delivered by popular nozzles at commonly used spray pressures. If the concentration is high enough, some surfactants can reduce the rebound of drops. With one surfactant, its concentration had to be much greater than the critical micelle concentration to reduce reflection of spray drops.