Growth Stage Affects Dose Response of Selected Glyphosate-Resistant Weeds to Premix of 2,4-D Choline and Glyphosate (Enlist Duo™ Herbicide*)

Parminder S Chahal,Kristin Rosenbaum,Amit J Jhala,Jatinder S Aulakh

doi:10.5539/jas.v7n11p1

Abstract

With the intent to control glyphosate–resistant and hard to control weeds, a formulation of 2,4-D choline (24.4%) and glyphosate (22.1%) (Enlist Duo™ herbicide) (Note 1) has been developed recently to be used post-emergence in corn and soybean tolerant to Enlist Duo™ in the United States. Dose response studies were conducted under greenhouse conditions for the evaluation of effective rates of Enlist Duo™ to control glyphosate-resistant common waterhemp (Amaranths rudis Sauer), giant ragweed (Ambrosia trifida L.), and kochia [Kochia scoparia (L.) Schrad] and to determine the effect of growth stage of these weeds on the efficacy of Enlist Duo™. Three parameter log-logistic models were used to develop dose response curves. Glyphosate-resistant giant ragweed was the most sensitive of the three weed species, followed by common waterhemp, and kochia. Based on the visual control or injury estimates, the Enlist Duo™ rates required for 90% control (ED90) of common waterhemp, giant ragweed, and kochia were 1179, 825, and 4,382 g ae ha -1 , respectively, for 10-cm tall plants compared to 2,480, 1,101, and 5,305 g ae ha -1 , respectively, for 20-cm tall plants at 21 days after treatment (DAT). The ED90 values calculated on the basis of percent shoot biomass reduction and visual control or injury estimates were usually similar at 21 DAT. The greenhouse studies indicate that Enlist Duo™ can effectively control less than or equal to 20-cm tall glyphosate-resistant giant ragweed and less than or equal to 10-cm tall glyphosate-resistant common waterhemp at the recommended rate (1,640 g ae ha -1 ).

Highlights

Simplified and economical weed management programs based on continuous and sole reliance on a single herbicide or herbicide(s) with the same mode(s) of action have resulted in the evolution of herbicide-resistant weeds (Beckie, 2011; VanGessel, 2001)
Several studies have reported that the height of weed species at the time of POST herbicide application is an important factor determining the level of control achieved (Chahal et al, 2014; Cordes et al, 2004; Craigmyle et al, 2013b)
Results of this study suggested that Enlist DuoTM herbicide is very effective for controlling glyphosate-resistant giant ragweed

Summary

Introduction

Simplified and economical weed management programs based on continuous and sole reliance on a single herbicide or herbicide(s) with the same mode(s) of action have resulted in the evolution of herbicide-resistant weeds (Beckie, 2011; VanGessel, 2001). The widespread cultivation of glyphosate-resistant crops since their introduction and commercialization in 1990’s and an almost exclusive reliance on glyphosate for POST weed control has raised issues of glyphosate-resistant weeds (Culpepper et al, 2006; Powles et al, 1998; VanGessel, 2001). As of 2014, 34 weed species have been confirmed resistant to glyphosate worldwide (Heap, 2015). Management of glyphosate-resistant weeds is the most significant predicament for growers (Culpepper et al, 2008; Johnson et al, 2009; Norsworthy et al, 2008; Price et al, 2011, 2012). Several weed management strategies have been recommended for controlling glyphosate-resistant weeds, including the use of tillage, cover crops, crop rotation, residual PRE herbicides, tank-mixing glyphosate with other modes of action herbicides, herbicide rotation or use of herbicides with different modes of action, and planting cultivars or crops resistant to www.ccsenet.org/jas

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