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Title: Evaporation and Deposition Coverage Area of Droplets Containing Insecticides and Spray Additives on Hydrophilic, Hydrophobic and Crabapple Leaf Surfaces

item YU, Y
item Zhu, Heping
item Derksen, Richard
item Krause, Charles

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2008
Publication Date: 2/3/2009
Citation: Yu, Y., Zhu, H., Derksen, R.C., Krause, C.R. 2009. Evaporation and Deposition Coverage Area of Droplets Containing Insecticides and Spray Additives on Hydrophilic, Hydrophobic and Crabapple Leaf Surfaces. Transactions of the ASABE. 52(1):39-49.

Interpretive Summary: Reduction of pesticide use has been emphasized as an important goal by the public due to the potential risks to human health and environment. However, the progress toward that goal has not been significantly achieved during the past decade. To realize greater pest control efficiency with less pesticide use, the combined efforts of application system performances, formulation of pest-control agents, plant surface fine structure, and microclimate conditions must be recognized and researched. Ignoring either the four factors can cause excessive pesticide use. In this research, the evaporation time and coverage area of droplets deposited on a waxy surface, a wax-free surface and crabapple leaves were investigated with different spray mixture additives, droplet sizes, and relative humidity condition. Adding the surfactant into spray mixtures resulted in a great decrease in droplet evaporation time and a great increase in maximal droplet coverage area while adding drift retardant into the spray mixtures resulted in a slight increase in droplet evaporation time but did not change the maximal coverage area. Droplets on the wax-free surface had a shorter evaporation time but larger coverage area than the droplets on the waxy surface. Increasing droplet size exponentially increased both droplet evaporation time and coverage area. However, increasing RH only increased droplet evaporation time but not droplet coverage area on targets. The information from this research is very useful for spray applicators, pesticide formulators and sprayer manufacturers to choose optimal spray techniques and formulating proper chemicals to maximize the pesticide spray application efficiency and minimize pesticide use.

Technical Abstract: The efficiency of foliar spray applications is influenced by the evaporation and residual pattern of pesticide droplets on targets. Evaporation time and maximal coverage area of a single droplet sizing from 246 to 886 µm at relative humidity (RH) ranging from 30 to 90% were measured with sequential images under controlled laboratory conditions. Droplets were placed inside an environmental-controlled chamber under a stereoscope and a high definition digital camera. The spray mixtures used to form droplets included different combinations of water, a nonionic colloidal polymer drift retardant, an alkyl polyoxyethylene surfactant, and two insecticides. The droplet evaporation was investigated on the surfaces of crabapple leaf surfaces, hydrophilic and hydrophobic glass slide surfaces, respectively. Adding surfactant into spray mixtures greatly increased droplet coverage area on the surfaces while droplet evaporation time was greatly reduced. For a 343 µm droplet on the crabapple leaf at 60% RH, the evaporation time decreased from 70 to 50 s and the maximal coverage area increased from 0.366 to 0.890 mm2 after the surfactant was added into the spray mixture containing water and insecticide. Adding the drift retardant into spray mixture slightly increased the droplet evaporation time and decreased the droplet coverage area. Also, changing the target surface from the hydrophilic slide to the hydrophobic slide greatly increased the droplet coverage area and reduced the droplet evaporation time. Increasing RH could increase the droplet evaporation time greatly but did not change the coverage area. The droplet evaporation time and coverage area increased exponentially as the droplet size increased. Therefore, droplet size, surface characteristics of the target (waxy or non-waxy), RH, and chemical composition of the spray mixture (water alone, pesticide, additives) should be included as important factors that can affect the efficacy and efficiency of pesticide applications.