A spray drift and associated vegetative vigor study was performed to link the amount of drift of a bare field herbicide application to impact on sensitive plants. Off-field deposition areas included bare ground (worst-case scenario), and typical field edge vegetation (12 inch mowed grass). Drift collectors were placed 5, 30, 50, 75, and 100 feet downwind of the application areas and were analyzed for the herbicide. Each trial employed four spray swaths (AIXR 11002 spray nozzle; wind speed 9.7-13.6 mph) perpendicular to the target wind direction and the downwind deposition/interception transects. Sensitive non-target plants (lettuce and navy beans; 2–4-true leaf growth stage, n=25) were placed in rows at 5, 30, 50 and 100 ft downwind of the application area. . The plants were moved to a greenhouse following spray application and plant survival, growth stage, phytotoxicity, and height were assessed at 7, 14 and 21 days after treatment (DAT) for all plants and at 28 DAT for lettuce. Biomass was determined at test termination. The results indicate much lower off-field deposition in the vegetated perimeter than in the bare field perimeter. Even in the worst-case scenario interception was 10% or less at 5 feet downwind and less than 1% at 50 feet and beyond. No effects occurred in either test species placed in edge vegetation at any distance. No statistical differences were observed in height or dry weight of either species at downwind distances of &gt;5 feet from the edge of a spray boom for bare ground trials. The study results demonstrate a markedly smaller impact area when compared with predicted effects zone derived by comparing modeled spray drift curves to greenhouse bioassay results, and suggests that the risk assessment based on greenhouse bioassays over-predicts effects on non-target plants at the field perimeter.

Assessment of spray drift and resulting plant effects in a non-target plant field study

2019 Fall National Meeting

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