Currently, plant canopy capture efficiency is not factored into the regulatory off-target drift risk assessments. For on-target applications, the pesticide application is carefully managed to optimize crop coverage by applying formulations with built-in adjuvants or tank-mixing with adjuvants to aid retention of spray droplets. These efforts take into consideration that plant species/canopy types have diverse morphology and surface characteristics, and as such will retain varying levels of applied pesticide loading. This concept is extendable to deposition of drifted spray droplets and the unique capture efficiency potential of off-target plants species, thus providing an opportunity to refine the current regulatory risk assessment practice where 100% drift interception and retention is assumed.     <br/> <br/>This work presents a methodology to quantify plant canopy capture efficiency using combined plant surface wettability potential, spray droplet characteristics and plant morphology data. These data coupled with modelling has the potential to improve scoping and design of non-target spray drift studies and to inform the risk assessment process.   <br/> <br/>We use wind tunnel experiments to demonstrate variability in spray drift capture efficiency between seven common field crops. We then use regression analysis of drift deposition rates to show the explanatory power of plant shape as the ratio of plant surface area to volume (derived from photogrammetry), and plant surface roughness (derived from Scanning Electron Microscope imagery). An application of ANSYS CFX (a computational fluid dynamics (CFD) modelling tool) to simulate the wind tunnel experiments is also presented, with model-predicted plant canopy efficiencies compared to measured canopy interception.

Modelling off-target plant canopy interception and surface retention of pesticide spray droplets

ACS Fall 2020 Virtual Meeting

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