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1 January 2017 Comparison of Herbicide Programs for Season-Long Control of Glyphosate-Resistant Common Waterhemp (Amaranthus rudis) in Soybean
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Abstract
The evolution of glyphosate and acetolactate synthase (ALS) inhibitor-resistant common waterhemp in the Midwestern United States has reduced the number of effective POST herbicide options for management of this problem weed in glyphosate-resistant soybean. Moreover, common waterhemp emerges throughout the crop growing season, justifying the need to evaluate herbicide programs that provide season-long control. The objectives of this study were to compare POST-only and PRE followed by (fb) POST herbicide programs for control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Field experiments were conducted in 2013 and 2014 in Dodge County, NE, in a field infested with glyphosate-resistant common waterhemp. Programs containing PRE herbicides resulted in ≥83% control of common waterhemp and densities of ≤35 plantsm−2 at 21 d after PRE (DAPRE). Post-only herbicide programs resulted in <70% control and densities of 107 to 215 plants m−2 at 14 d after early-POST (DAEPOST) treatment. PRE fb POST herbicide programs, including saflufenacil plus imazethapyr plus dimethenamid-P, sulfentrazone plus cloransulam, or S-metolachlor plus metribuzin, fb fomesafen plus glyphosate; S-metolachlor plus fomesafen fb acifluorfen plus glyphosate resulted in >90% control of glyphosate-resistant common waterhemp throughout the growing season, reduced density to ≤7plantsm−2, ≥92% biomass reduction, and soybean yield >2,200kg ha−1. Averaged across herbicide programs, common waterhemp control was 84%, and density was 15 plants m−2 with PRE fb POST herbicide programs compared with 42% control, and density of 101 plants m−2 with POST-only herbicide programs at harvest. Results of this study indicated that PRE fb POST herbicide programs with effective modes of action exist for season-long control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean.Nomenclature: Acetochlor; acifluorfen; chlorimuron-ethyl; cloransulam-methyl; dimethenamid-P; flumioxazin; fomesafen; glyphosate; imazethapyr; lactofen; saflufenacil; S-metolachlor; sulfentrazone; thifensulfuron-methyl; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr.La evolución de Amaranthus rudis resistente a glyphosate y a inhibidores de acetolactate synthase en el medio oeste de los Estados Unidos ha reducido el número de opciones efectivas de herbicidas POST para el manejo de esta problemática maleza en soja resistente a glyphosate. Además, A. rudis emerge a lo largo de la temporada de crecimiento del cultivo, lo que justifica la necesidad de evaluar programas de herbicidas que brinden control durante toda la temporada. Los objetivos de este estudio fueron comparar programas con sólo herbicidas POST y con herbicidas PRE seguidos por (fb) herbicidas POST para el control de A. rudis resistente a glyphosate en soja resistente a glyphosate. Se realizaron experimentos de campo en 2013 y 2014 en el condado Dodge, en Nebraska, en campos infestados con A. rudis resistente a glyphosate. Los programas que contenían herbicidas PRE resultaron en ≥83% de control de A. rudis y en densidades de ≤35 plantas m−2 a 21 d después de PRE (DAPRE). Programas con sólo herbicidas POST resultaron en <70% de control y densidades de 107 a 215 plantas m−2 a 14d después del tratamiento POST temprano (DAEPOST). Programas de herbicidas PRE fb POST, incluyendo saflufenacil más imazethapyr más dimethenamid-P, sulfentrazone más cloransulam, o S-metolachlor más metribuzin, fb fomesafen más glyphosate; S-metolachlor más fomesafen fb acifluorfen más glyphosate resultaron en >90% de control de A. rudis resistente a glyphosate a lo largo de la temporada, densidad reducida a ≤7 plantas m−2, reducción de biomasa ≥92%, y rendimiento de soja >2,200 kg ha−1. Promediando los programas de herbicidas, el control de A. rudis al momento de la cosecha fue 84%, y la densidad fue 15 plantas m−2 con programas de herbicidas PRE fb POST en comparación con 42% de control y densidad de 101 plantas m
© Weed Science Society of America, 2017 
Debalin Sarangi, Lowell D. Sandell, Greg R. Kruger, Stevan Z. Knezevic, Suat Irmak and Amit J. Jhala "Comparison of Herbicide Programs for Season-Long Control of Glyphosate-Resistant Common Waterhemp (Amaranthus rudis) in Soybean," Weed Technology 31(1), (1 January 2017). https://doi.org/10.1017/wet.2016.1
Received: 24 November 2015; Accepted: 22 September 2016; Published: 1 January 2017
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