Response of Amaranthus spp. following exposure to sublethal herbicide rates via spray particle drift.

Bruno C Vieira,Joe D Luck,Todd A Gaines,Greg R Kruger,Rodrigo Werle,Keenan L Amundsen

doi:10.1371/journal.pone.0220014

Bruno C Vieira, Joe D Luck + Show 4 more

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https://doi.org/10.1371/journal.pone.0220014

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Abstract

The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature. However, little to no information is available on the consequences of herbicide drift onto weed species inhabiting boundaries of agricultural fields. Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved herbicide-resistance after recurrent selection with sublethal herbicide rates This study investigated the deposition of glyphosate, 2,4-D, and dicamba spray particle drift from applications with two different nozzles in a low speed wind tunnel, and their impact on growth and development of Amaranthus spp. Herbicide drift resulted in biomass reduction or complete plant mortality. Inflection points (distance to 50% biomass reduction) for Amaranthus tuberculatus were 7.7, 4.0, and 4.1 m downwind distance for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 2.8, 2.5, and 1.9 m for applications with the air-inclusion nozzle. Inflection points for Amaranthus palmeri biomass reduction were 16.3, 10.9, and 11.5 m for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 7.6, 5.4, and 5.4 m for applications with the air-inclusion nozzle. Plants were more sensitive to glyphosate at higher exposure rates than other herbicides, whereas plants were more sensitive to 2,4-D and dicamba at lower exposure rates compared to glyphosate. Applications with the flat-fan nozzle resulted in 32.3 and 11.5% drift of the applied rate at 1.0 and 3.0 m downwind, respectively, whereas the air-inclusion nozzle decreased the dose exposure in the same distances (11.4 and 2.7%, respectively). Herbicide drift towards field boundaries was influenced by nozzle design and exposed weeds to herbicide rates previously reported to select for herbicide-resistant biotypes.

Highlights

Spray drift is defined as the part of the application that is deflected away from the target during or following applications [1]
Little to no information is available on the consequences of herbicide drift on agricultural weed species
Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved resistance after recurrent selection with sublethal herbicide rates [18,19,20,21,22,23,24,25,26,27]

Summary

Introduction

Spray drift is defined as the part of the application (particles or vapors) that is deflected away from the target during or following applications [1]. Spray droplet size which is directly influenced by nozzle design, nozzle orifice size, operating pressure, and physicochemical properties of the solution, is often the focal point of particle drift mitigation efforts [5,6,7]. Risk assessment of herbicide drift includes the surrounding vegetation characterization, as nontarget sensitive vegetation coexist with agricultural fields [8,9]. The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature [10,11,12,13]. Little to no information is available on the consequences of herbicide drift on agricultural weed species. Weed species including horseweed (Erigeron canadensis L.), waterhemp [Amaranthus tuberculatus (Moq.) J. AMBTR), and others are often abundant in field boundaries and ditches surrounding agricultural lands in the US Midwest [14,15,16,17] (Fig 1)

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