Growth and Yield Losses of Roundup Ready Soybean as Influenced by Micro-rates of 2,4-D

Ivan Cuvaca,Stevan Knezevic,Jon Scott,O Adewale Osipitan

doi:10.5539/sar.v10n4p27

Abstract

Widespread resistance to glyphosate has made weed control very challenging. In response, new approaches to managing resistant biotypes such as the Enlist E3TM have been developed. This technology allows in-crop use of 2,4-D but there is fear associated with unintentional application of the herbicide (e.g. direct application, tank contamination, or spray drift) to sensitive crops. A study was conducted to evaluate Roundup Ready (RR) soybean growth and yield loss as influenced by 2,4-D [six micro rates of 1/5, 1/10, 1/50, 1/100, 1/500 and 1/1000 of the 1,120 g ae ha-1 label recommended dose, and a check with no herbicide applied] applied at V2, R1 and R2 growth stages. In general, RR soybean was more sensitive to 2,4-D at R1 than V2 and R2. The highest 2,4-D rate, 1/5 of the label recommended rate, caused 51% soybean injury symptom, 13 d canopy closure delay, 41.2% plant height reduction, and 68.9% yield loss at R1. Based on effective dose (ED) estimates, 37.7 g ae ha-1 2,4-D caused 5% yield loss (0.23 Mg ha-1) at R1 compared with a 2.5- and 2.0-fold higher dose at V2 and R2, respectively. With respect to number of days to canopy closure, both reproductive stages (R1 and R2) were equally less sensitive to 2,4-D than the vegetative one (V2) as the plants had already achieved maximum growth recorded. On the other hand, ED estimates for plant height have shown that both V2 and R2 were equally more sensitive to 2,4-D than R1. These results clearly indicated that RR soybean growth and yield loss were significantly influenced by the timing of exposure and amount of 2,4-D.

Highlights

The discovery of auxin type herbicides has revolutionized agriculture by shaping the way we farm in much of the world
Soybean injury symptoms increased with increase in 2,4-D micro-rate regardless of soybean growth stage at time of herbicide application
Increasing 2,4-D dose from 1/1000 to 1/5 of the label recommended dose resulted in soybean injury ranging from 0 to 48% at V2, 0 to 51% at R1, and 0 to 36% at R2 at 21 days after treatment (DAT), respectively

Summary

Introduction

The discovery of auxin type herbicides has revolutionized agriculture by shaping the way we farm in much of the world. Since their introduction in the mid-1940s, auxin herbicides have become one of the most widely used group of herbicides and an integral component of major North America cropping systems. If further selection for synthetic auxins resistant biotypes is to be slowed, a more responsible use of these herbicides must be considered. This is especially relevant with the recent introduction of synthetic auxin tolerant crops in the U.S One such example is the Enlist E3 soybean. These compounds contain 2,4-D choline, which has the potential to http://sar.ccsenet.org

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