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This article reviews approaches to analytical pesticide deposition modeling for aerial, ground boom, and orchard airblast sprayer applications, and describes modeling approaches including the Lagrangian model commonly used for aerial spraying, which tracks the mean position and standard deviation of spray material released into the ambient environment. This review also describes the approaches used in mechanistic ground sprayer modeling, including near-nozzle effects and spray sheet obstruction of the ambient flow. The random-walk approach for ground spraying and the significant computational fluid dynamics (CFD) problem associated with modeling orchard airblast spraying are also described. These mechanistic approaches predict the spray deposition downwind from an application area for any set of initial conditions, and can recover results consistent with field datasets. Incorporation of spray deposition modeling into a Geographic Information System (GIS) platform is also discussed.

The development of the aerial spray dispersion model FSCBG (Forest Service, Cramer, Barry and Grim) by the USDA Forest Service and the U.S. Army is reviewed. FSCBG predicts the behavior of spray material released through nozzles into the wake of a spray aircraft (helicopter or fixed-wing), traveling through idealized atmospheric effects, penetrating a canopy and depositing on the ground. FSCBG contains simplified models for the complex flow structure behind aircraft and the mechanisms that affect the fate of aerially released material: downwind drift, evaporation, canopy penetration, and ground and canopy deposition. Model development efforts encompass the areas of spray behavior, aircraft wake effects, meteorological influences, canopy interaction, and deposition. These efforts are supplemented by model validation with field tests. The ability of the model to quantify off-target spray drift is particularly important.