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1 October 2015 Control of Johnsongrass in the Absence of Glyphosate in Midsouth Cotton Production Systems
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Johnsongrass populations that are resistant to 5-enolpyruvyl-3-shikimate synthase (EPSPS)–, acetyl coenzyme A carboxylase (ACCase)–, or acetolactate synthase (ALS)–inhibiting herbicides are increasingly common throughout the midsouth. Three trials were conducted in 2012, 2013, and 2014 in Fayetteville, AR and Alexandria, LA to evaluate strategies with and without ALS- and ACCase inhibitors for management of rhizomatous johnsongrass in the absence of glyphosate. Fluometuron or fluometuron plus pyrithiobac applied PRE followed by (fb) EPOST, MPOST, and LAYBY tank mixtures containing multiple effective mechanisms of action (MOA) controlled johnsongrass at least 90%. Simplifying the program by removing a herbicide or eliminating an application timing reduced control, and increased vegetative and sexual reproduction of johnsongrass. To manage severe infestations or escapes glufosinate plus clethodim fb glufosinate plus clethodim or clethodim plus pyrithiobac fb clethodim) effectively controlled 15-cm johnsongrass. However, johnsongrass control was reduced when ALS and ACCase inhibitors were tank mixed, especially for the second POST application, compared to ACCase inhibitors alone. Effective herbicide programs are available to growers to control johnsongrass in the absence of glyphosate, but the use of PRE herbicides followed by multiple applications of POST herbicides is critical for successful management.

Nomenclature: Clethodim, fluometuron, glufosinate, pyrithiobac, johnsongrass, Sorghum halepense L.; cotton, Gossypium hirsutum L.

Las poblaciones de Sorghum halepense que son resistentes a herbicidas inhibidores de 5-enolpyruvyl-3-shikimate synthase (EPSPS), acetyl coenzyme A carboxylase (ACCase), o acetolactate synthase (ALS) están aumentando a lo largo del sur medio de los Estados Unidos. Se realizaron tres ensayos en 2012, 2013, y 2014 en Fayetteville, Arkansas y en Alexandria, Louisiana, para evaluar estrategias con y sin inhibidores de ALS y ACCase para el manejo de S. halepense con rizomas en ausencia de glyphosate. Fluometuron o fluometuron más pyrithiobac aplicados PRE seguidos de (fb) aplicaciones EPOST, MPOST, y a la base del cultivo antes del cierre del dosel (LAYBY) con mezclas en tanque conteniendo múltiples mecanismos de acción (MOA) controlaron S. halepense al menos 90%. El simplificar el programa removiendo un herbicida o eliminando un momento de aplicación redujo el control e incrementó la reproducción vegetativa y sexual de S. halepense. Para manejar infestaciones severas o escapes, glufosinate más clethodim fb glufosinate más clethodim o clethodim más pyrithiobac fb clethodim controlaron efectivamente S. halepense de 15 cm de altura. Sin embargo, el control de S. halepense se redujo cuando los inhibidores ALS y ACCase fueron mezclados en tanque, especialmente en la segunda aplicación POST, al compararse con inhibidores de ACCase solos. Los productores cuentas con programas efectivos de herbicidas para el control de S. halepense en ausencia de glyphosate, pero el uso de herbicidas PRE seguido de múltiples aplicaciones de herbicidas POST es crítico para un manejo exitoso.

Christopher J. Meyer, Jason K. Norsworthy, Daniel O. Stephenson IV, Mohammad T. Bararpour, Randall L. Landry, and Brandi C. Woolam "Control of Johnsongrass in the Absence of Glyphosate in Midsouth Cotton Production Systems," Weed Technology 29(4), 730-739, (1 October 2015).
Received: 24 April 2015; Accepted: 1 July 2015; Published: 1 October 2015

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