The Practical Use of Agdrift® and Other Drift Exposure Models for Aerial, Ground and Orchard Spray Applications

The practical use of spray drift databases and models for predicting drift exposure in pesticide applications is discussed. The AgDRIFT® model, developed by government and industry scientists in the US facilitates such assessments for various application scenarios. Aerial applications can be modelled using a predictive model that considers the effects of application, tank mix, meteorological and environmental variables on off-target spray movements and deposition. Such assessments can be made at three different tier levels, each allowing access to more of the input variables than the preceding lower tier level. The lowest tier level allows specification of spray quality, while higher tiers allow access to variables such as release height, wind speed and other variables. Ground rig application scenarios are currently modelled as curve fits of field data allowing spray quality and release height to be assessed for different numbers of spray swaths. Orchard airblast applications are included at the lowest tier level for different sprayer and canopy types, with the default setting including composite orchard and vine canopies. Predictive models are being developed for higher tier level assessments for spray applications by ground rig and orchard airblast equipment. An atomization model has also been developed to predict droplet size for applications of tank mixes with user-defined or reasonable worst-case physical properties through a wide range of hydraulic nozzle types applicable to aerial applications. This model, DropKick® is included within AgDRIFT® or as a stand-alone model. Other atomization models are also available within AgDRIFT® for predicting droplet size of nozzles types that have been tested by the United States Dept. of Agriculture (USDA). These and other models are described in the present paper with a particular emphasis on drift exposure assessments.