Cotton growers rely heavily upon glufosinate and various residual herbicides applied preplant, PRE, and POST to control Palmer amaranth resistant to glyphosate and acetolactate synthase-inhibiting herbicides. Recently deregulated in the United States, cotton resistant to dicamba, glufosinate, and glyphosate (B2XF cotton) offers a new platform for controlling herbicide-resistant Palmer amaranth. A field experiment was conducted in North Carolina and Georgia to determine B2XF cotton tolerance to dicamba, glufosinate, and glyphosate and to compare Palmer amaranth control by dicamba to a currently used, nondicamba program in both glufosinate- and glyphosate-based systems. Treatments consisted of glyphosate or glufosinate applied early POST (EPOST) and mid-POST (MPOST) in a factorial arrangement of treatments with seven dicamba options (no dicamba, PRE, EPOST, MPOST, PRE followed by [fb] EPOST, PRE fb MPOST, and EPOST fb MPOST) and a nondicamba standard. The nondicamba standard consisted of fomesafen PRE, pyrithiobac EPOST, and acetochlor MPOST. Dicamba caused no injury when applied PRE and only minor, transient injury when applied POST. At time of EPOST application, Palmer amaranth control by dicamba or fomesafen applied PRE, in combination with acetochlor, was similar and 13 to 17% greater than acetochlor alone. Dicamba was generally more effective on Palmer amaranth applied POST rather than PRE, and two applications were usually more effective than one. In glyphosate-based systems, greater Palmer amaranth control and cotton yield were obtained with dicamba applied EPOST, MPOST, or EPOST fb MPOST compared with the standard herbicides in North Carolina. In contrast, dicamba was no more effective than the standard herbicides in the glufosinate-based systems. In Georgia, dicamba was as effective as the standard herbicides in a glyphosate-based system only when dicamba was applied EPOST fb MPOST. In glufosinate-based systems in Georgia, dicamba was as effective as standard herbicides only when dicamba was applied twice.

Nomenclature: Acetochlor; dicamba; diuron; fomesafen; glufosinate; glyphosate; MSMA; pyrithiobac; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L.

Los productores de algodón dependen mucho del uso de glufosinate y de varios herbicidas residuales aplicados pre-siembra, PRE, y POST, para el control de Amaranthus palmeri resistente a glyphosate y resistente a herbicidas inhibidores de acetolactate synthase. Recientemente desregulado en los Estados Unidos, el algodón resistente a dicamba, glufosinate, y glyphosate (algodón B2XF) ofrece una nueva plataforma para el control de A. palmeri resistente a herbicidas. En North Carolina y Georgia, se realizó un experimento de campo para determinar la tolerancia de B2XF a dicamba, glufosinate, y glyphosate y para comparar el control de A. palmeri con dicamba con un programa actualmente usado (sin dicamba) en sistemas basados en glufosinate y glyphosate. Los tratamientos de glyphosate y glufosinate aplicados POST temprano (EPOST) y POST medio (MPOST) en un arreglo factorial de tratamientos con siete opciones de dicamba (sin dicamba, PRE, EPOST, MPOST, PRE seguido de [fb] EPOST, PRE fb MPOST, y EPOST fb MPOST) y un estándar sin dicamba. El estándar sin dicamba consistió en fomesafen PRE, pyrithiobac EPOST, y acetochlor MPOST. Dicamba no causó ningún daño cuando se aplicó PRE y solamente un daño menor y temporal cuando se aplicó POST. Al momento de la aplicación EPOST, el control de A. palmeri con dicamba o fomesafen aplicados PRE, en combinación con acetochlor fue similar, y fue de 13 a 17% mayor al de acetochlor solo. Dicamba fue generalme