Abstract
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.
Highlights
Herbicide treatment in crops by aerial application is imperative in regions with frequent rainfall and wet soils (Reddy et al, 2010)
The analysis of variance (ANOVA) results showed a significant difference between the distances evaluated for the phytotoxicity level from the application area (Figure 1)
On average, plants established at distances more than 338 m showed a phytotoxicity level less than 50% at the 8th day after treatment (DAT) after the drift occurrence, while plants established at a distance more than 777 m had this same injury level in the second evaluation (14th DAT)
Summary
Herbicide treatment in crops by aerial application is imperative in regions with frequent rainfall and wet soils (Reddy et al, 2010). During pre-sowing management of irrigated riceland, non-selective herbicides are necessary for the burndown of vegetation present in the areas. In areas with soybean rotation, presowing management begins with the total removal of the existing vegetation. In the Rio Grande do Sul (RS) State, Brazil’s leading rice producer, rice/soybean rotation areas have increased in the last decade. In 2009, the total cultivated area was 11,150 hectares, and during the 2016-2017 season, 297,453 hectares (IRGA, 2018). Almost all of these areas are seeded with glyphosate-resistant soybean cultivars due to the possibility of eliminating postemergent weeds from the crops at a low cost (Duke and Powles, 2008)
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