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A field spray drift study to determine the downwind effects of isoxaflutole herbicide to nontarget plants.

ABSTRACT: Spray drift buffers are often required on herbicide labels to prevent potential drift effects to nontarget plants. Buffers are typically derived by determining the distance at which predicted exposure from spray drift equals the ecotoxicology threshold for sensitive plant species determined in greenhouse tests. Field studies performed under realistic conditions have demonstrated, however, that this approach is far more conservative than necessary. In 2016, the US Environmental Protection Agency estimated that isoxaflutole (IFT), a herbicide used to control grass and broadleaf weeds, could adversely affect downwind nontarget dicot plants at distances of ≥304 m from the edge of the treated field due to spray drift. This prediction implies that a buffer of at least 304 m is required to protect nontarget plants. To refine the predicted buffer distance for IFT, we conducted a field study in which sensitive nontarget plants (lettuce and navy bean, two to four leaf stage) were placed at various distances downwind from previously harvested soybean fields sprayed with Balance^® Flexx Herbicide. The test plants were then transported to a greenhouse for grow out following the standard vegetative vigor test protocol. There were three trials. One had vegetation in the downwind deposition area (i.e., test plants placed in mowed grass; typical exposure scenario) and two had bare ground deposition areas (worst-case exposure scenario). For both plant species in bare ground deposition areas, effects on shoot height and weight were observed at 1.52 m but not at downwind distances of ≥9.14 m from the edge of the treated area. No effects were observed at any distance for plants placed in the vegetated deposition area. The field study demonstrated that a buffer of 9.14 m protects nontarget terrestrial plants exposed to IFT via spray drift even under worst-case conditions. Integr Environ Assess Manag 2022;18:757-769. © 2021 Bayer. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

SUBMITTER: Moore DRJ

PROVIDER: S-EPMC9293113 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:During herbicide spray application, nontarget terrestrial plants (NTTPs) growing in the off-field area need to be protected from unacceptable effects of herbicide drift. The risk of such unintended effects is assessed in order to establish whether a particular use can be approved, possibly in combination with mitigation measures. In Europe, the risk of herbicide treatment to NTTPs is assessed on the basis of tier 2 studies done under controlled conditions in greenhouses. Following the concept of a tiered testing approach, higher tier field studies under more realistic conditions could be used to refine the risk assessment. No current guideline for conducting higher tier NTTP field studies is available. We developed an NTTP higher tier field study method done on an experimental plant community established by sowing of a seed mixture. The setup was optimized in 3 pilot field studies and subsequently used for a definitive study testing effects of the herbicide iofensulfuron-sodium. Results show that the method can be regarded as a suitable higher tier option for assessing effects of herbicides on NTTPs. Growth of species from the soil seed bank cannot be avoided and has to be carefully considered when evaluating results. Adaptations of the study design may be necessary when testing different herbicides. Community-level endpoints were at the same level as single-species endpoints. Results of the field study were compared to standard greenhouse study results for the same herbicide. No observed effect rates (NOERs) in the field were about a factor of 10 higher and show that the current tier 2 risk assessment for NTTPs can be regarded as protective in this case. Whether the present field study design and the assessed endpoints can be used in higher tier risk assessment of NTTPs depends on selection of the specific protection goal and requires further discussion. Integr Environ Assess Manag 2020;16:691-705. © 2020 Bayer AG. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Project description:Pesticide spray drift represents an important exposure pathway that may cause illness among orchard workers. To strike a balance between improving spray coverage and reducing drift, new sprayer technologies are being marketed for use in modern tree canopies to replace conventional axial fan airblast (AFA) sprayers that have been used widely since the 1950s. We designed a series of spray trials that used mixed-effects modeling to compare tracer-based drift volume levels for old and new sprayer technologies in an orchard work environment. Building on a smaller study of 6 trials (168 tree rows) that collected polyester line drift samples (n = 270 measurements) suspended on 15 vertical masts downwind of an AFA sprayer application, this study included 9 additional comparison trials (252 tree rows; n = 405 measurements) for 2 airblast tower sprayers: the directed air tower (DAT) and the multi-headed fan tower (MFT). Field-based measurements at mid (26 m) and far (52 m) distances showed that the DAT and MFT sprayers had 4-15 and 35-37% less drift than the AFA. After controlling for downwind distance, sampling height, and wind speed, model results indicated that the MFT [-35%; 95% confidence interval (CI): -22 and -49%; P < 0.001] significantly reduced drift levels compared to the AFA, but the DAT did not (-7%; 95% CI: -19 and 6%; P = 0.29). Tower sprayers appear to be a promising means by which to decrease drift levels through shorter nozzle-to-tree canopy distances and more horizontally directed aerosols that escape the tree canopy to a lesser extent. Substitution of these new technologies for AFA sprayers is likely to reduce the frequency and magnitude of pesticide drift exposures and associated illnesses. These findings, especially for the MFT, may fit United States Environmental Protection Agency's Drift Reduction Technology (DRT) one-star rating of 25-50% reduction. An 'AFA buyback' incentive program could be developed to stimulate wider adoption of new drift-reducing spray technologies. However, improved sprayer technologies alone do not eliminate drift. Applicator training, including proper sprayer calibration and maintenance, and application exclusion zones (AEZs) can also contribute to minimizing the risks of drift exposure. With regard to testing DRTs and establishing AEZs, our study findings demonstrate the need to define the impact of airblast sprayer type, orchard architecture, sampling height, and wind speed.

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A field spray drift study to determine the downwind effects of isoxaflutole herbicide to nontarget plants.

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