Drift Distance in Aircraft Glyphosate Application Using Rice Plants as Indicators

ABSTRACT: This study aimed to evaluate the potential for glyphosate drift during aerial application using rice plants as sentinels, aiming to determine the effect of drift on irrigated rice crops. For this purpose, a field experiment was performed using an entirely randomized design with four replicates, evaluating different distances from the site of application [control (no application), 0, 12.5, 25, 50, 75, 100, 150, 200, 300, and 400 m]. The experiment was carried out at the Granjas 4 Irmãos farm, located in the Rio Grande city, Rio Grande do Sul State, Brazil. The glyphosate dose application was 1,920 g e.a. ha-1 (Roundup Transorb®, 480 g e.a. L-1 glyphosate isopropylamine salt). A dose-response curve was developed to estimate the drift rate in sentinel plants, by applying increasing glyphosate doses in rice plants and assessing the injury level. The drift rates estimated by the injury level in sentinel plants were 14% (150 m), 13% (200 m), and 5% (400 m). Death of the experimental units was observed for distances between 0 and 50 m, while in distances between 75 and 150 m, 25 to 50% of the plants survived, reducing productivity. In the distances between 200 and 400 m, there was no reduction in productivity when compared to the control, even when the injury levels reached 52 to 82%. Thus, we concluded that a 5% glyphosate drift reached up to 400 m from the application range. Considering the recommendation of zero drift, distances greater than 400 m should be adopted to avoid symptoms in rice plants. We suggest using distances of more than 400 m in future studies.