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item Hoffmann, Wesley

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/12/2004
Publication Date: 10/20/2004
Citation: Hoffmann, W.C. Crop and canopy effects of spray deposition and drift [abstract]. Proceedings of the International Conference on Pesticide Application for Drift Management, October 27-29, 2004, Waikoloa, Hawaii. 2004 CDROM.

Interpretive Summary:

Technical Abstract: Many factors influence the deposition and movement of aerially applied crop protection chemicals. Besides meteorological conditions and application parameters, the structure of the spray target can significantly impact where spray droplets deposit. Studies were conducted to investigate the influence that crop canopies, such as corn, cotton, and soybeans, have on spray deposition and movement. Using a fluorescent dye as a tracer, spray deposits were measured at the top of the canopy (TOP samples), at the ground within the crop canopy (GROUND samples), and in a grazed pasture (PASTURE samples). Additional studies were conducted to compare field-collected data to AGDISP model predictions. The effects of meteorological conditions, surface roughness coefficient, and crop height on downwind spray movement were determined and reported. In the near field (0-40 m (0-131 ft)) samples, TOP deposition was higher than the PASTURE samples in corn, cotton, and soybeans, except at 0 and 5 m in cotton. In the field experiments, wind speed did not consistently influence the spray deposition and movement. There were good correlations between the spray flux (amount of material moving downwind from an aerial application) as measured by samplers in the field and the spray flux predicted by the AGDISP model. The impact of surface roughness coefficients was minimal in terms of downwind spray movement. However, a 2 m/sec increase in wind speed resulted in a 4-fold increase in the spray flux at 50 m from the application site. When crop height changed from 0.3 m to 1.3 m, the spray flux decreased by 10-fold, demonstrating the dramatic filtering effect that a canopy can have on a spray cloud.