Response of Soybean Offspring to a Dicamba Drift Event the Previous Year

Gordon T Jones,Jason K Norsworthy,Tom Barber

doi:10.1017/wet.2019.2

Abstract

AbstractIn the occurrence of dicamba drift, it is not well understood what measurements from soybean plants would correlate with damage to soybean offspring; therefore, possible relationships are of great interest. Sixteen drift trials were established in 2014 and 2015 at the Northeast Research and Extension Center in Keiser, AR. A single 8-m-wide by 30- or 60-m-long pass with a high-clearance sprayer was made in each soybean field, resulting in a dicamba drift event. Seeds were collected from plants in each drift trial and planted in the field in 2015 and 2016. Data were subjected to correlation analysis to determine pairwise associations among parent and offspring observations. Auxin-like symptomology in offspring consistent with dicamba, primarily as leaf cupping, appeared in plots at the unifoliate and first trifoliate stages. Auxin-like symptoms were more prevalent in offspring collected from plants from later reproductive stages as opposed to early reproductive stages. The highest correlation coefficients occurred when parent plants were treated at the R5 growth stage. Parent mature pod malformation was correlated with offspring emergence (r=−0.37, P=0.0082), vigor (r=−0.57, P ≤ 0.0001), injury (r=0.93, P ≤ 0.0001), and percent of plants injured (r=0.92, P ≤ 0.0001). This research documents that soybean damaged from dicamba drift during the R1 to R6 growth stages can negatively affect offspring and that occurrence of pod malformation after dicamba drift at the R5 growth stage may be indicative of injury to the offspring.

Highlights

Labeling of additional dicamba-containing herbicides for over-the-top use in dicambaresistant (DR) cotton (Gossypium hirsutum L.) and soybean (Anonymous 2016a, 2016b) will increase the amount and frequency of dicamba application
When DR soybean and cotton are planted adjacent to non-DR soybean, applicators must be aware of factors that could contribute to off-target movement due to high sensitivity of non-DR soybean, because rates as low as 0.08 g ae ha − 1 may cause visible injury symptoms consistent with auxin herbicides (Weidenhamer et al 1989)
Field drift experiments were conducted in 2014 and 2015 at the University of Arkansas Northeast Research and Extension Center (NEREC) in Keiser, AR, and offspring experiments were completed at the Arkansas Agricultural Research and Extension Center (AAREC) in Fayetteville, AR, in 2015 and 2016

Summary

Introduction

Labeling of additional dicamba-containing herbicides for over-the-top use in dicambaresistant (DR) cotton (Gossypium hirsutum L.) and soybean (Anonymous 2016a, 2016b) will increase the amount and frequency of dicamba application. When DR soybean and cotton are planted adjacent to non-DR soybean, applicators must be aware of factors that could contribute to off-target movement due to high sensitivity of non-DR soybean, because rates as low as 0.08 g ae ha − 1 may cause visible injury symptoms consistent with auxin herbicides (Weidenhamer et al 1989). Proper boom height, proper spray pressure, and approved mixtures will aid in keeping dicamba from moving off-target via physical drift to susceptible soybean (Anonymous 2017a, 2017b; Maybank et al 1978; Wolf et al 1992)

Objectives

Methods

Results