Off-Target Movement of Diglycolamine Dicamba to Non-dicamba Soybean Using Practices to Minimize Primary Drift

Gordon T Jones,Tom Barber,Jason K Norsworthy

doi:10.1017/wet.2018.90

Gordon T Jones, Tom Barber + Show 1 more

Open Access

https://doi.org/10.1017/wet.2018.90

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Journal: Weed Technology	Publication Date: Jan 18, 2019
Citations: 22	License type: CC BY 4.0

Affiliation: University of Arkansas at Fayetteville

Abstract

AbstractSoybean with resistance to dicamba (DR soybean) and glyphosate and cotton with resistance to glyphosate, glufosinate, and dicamba were recently commercialized in the United States and have been readily adopted. To evaluate results of over-the-top application of dicamba in DR crops, field studies were designed to examine off-target movement using proposed sprayer setup recommendations. Association analysis and nonlinear regression techniques were used to examine the effects of 26 field-scale drift trials conducted in 2014 and 2015 during soybean reproductive development (R1 through R6). The greatest predictors (injury, height reduction) of soybean yield reduction generally occurred and had steeper relationships after drift events at the R1 growth stage than at later stages. Using non-DR soybean as an indicator, dicamba was documented to move as much as 152 m from the application area (distance to 5% injury). Instances of height reduction (5%) differed among growth stages, with the greatest distance occurring at R1 (83.4 m). Soybean yield reduction was erratic, with the greatest distance to 5% loss in yield occurring at 42.8 m after an R1 drift event. Overall, the data suggest flowering-stage soybean is more sensitive than later reproductive soybean to injury, height reductions, and yield loss. Average and maximum wind speeds did not account for the injury documented from dicamba, and it is hypothesized that other meteorological variables also play a notable role in dicamba off-target movement as well as growing conditions following exposure. With concerns surrounding off-target movement of dicamba, proper stewardship of this new technology will be key to its longevity.

Highlights

With herbicide resistance continuing to spread across the United States in weeds such as Palmer amaranth
Watson), waterhemp (Amaranthus spp.), and horseweed [Conyza canadensis (L.) Cronq.], there is a need for new herbicides to provide control of these broadleaf weeds in soybean and cotton (Heap 2017; Kruger et al 2010; Meyer et al 2015)
Many regulations have been enacted pertaining to these variables for dicamba application in DR soybean and cotton to limit off-target movement of the herbicide (Anonymous 2017c, 2017d)

Summary

Introduction

With herbicide resistance continuing to spread across the United States in weeds such as Palmer amaranth Watson), waterhemp (Amaranthus spp.), and horseweed [Conyza canadensis (L.) Cronq.], there is a need for new herbicides to provide control of these broadleaf weeds in soybean and cotton (Heap 2017; Kruger et al 2010; Meyer et al 2015). Research has documented that dicamba will effectively control these problem weeds and others when used properly in DR cotton and soybean (Byker et al 2013; Cahoon et al 2015). Off-target movement of herbicide to susceptible crops is of concern. Many regulations have been enacted pertaining to these variables for dicamba application in DR soybean and cotton to limit off-target movement of the herbicide (Anonymous 2017c, 2017d). Lack of applicator training could still result in misapplications, uninformed applicators are not the sole cause of misapplication (Bish and Bradley 2017)

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