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Glyphosate-Resistant Common Waterhemp (Amaranthus rudis) Confirmed in Texas

Published online by Cambridge University Press:  20 January 2017

G. G. Light
Department of Plant and Soil Science, Box 42122, Texas Tech University, Lubbock, TX 79409-2122
M. Y. Mohammed
Borlaug Institute for International Agriculture—Texas A&M University System, 2477 TAMU, College Station, TX 77843-2477
P. A. Dotray
Department of Plant and Soil Science, Texas Tech University, Texas AgriLife Research, and Texas AgriLife Extension, Box 42122 Lubbock, TX 79409-2122
J. M. Chandler
Department of Soil and Crop Sciences, Texas A&M University, 2474 TAMU, College Station, TX 77843-2474
R. J. Wright*
Department of Plant and Soil Science, Texas Tech University and Texas AgriLife Research, Box 42122, Lubbock, TX 79409
Corresponding author's E-mail:


Glyphosate-resistant Amaranthus species are a recognized risk to U.S. agriculture. With affected cropland exceeding 1.2 million ha, this epidemic is particularly pertinent to agricultural regions that utilize an intensive glyphosate-based management program to control weedy pests. Before 2006, Texas had no identified glyphosate-resistant populations. Two independent common waterhemp populations exhibiting poor control by glyphosate were identified in Wharton County and Fort Bend County, TX in 2006 and 2008, respectively. The objective of the present research was to characterize the level of glyphosate resistance (50% lethal dose [LD50] and 50% reduction in growth rate [GR50]) in each population. Resistance levels in four putatively glyphosate-resistant common waterhemp biotypes selected from these two populations were compared with confirmed glyphosate-resistant and -susceptible common waterhemp populations under greenhouse conditions. The LD50 value for the susceptible population (736 g ae ha−1) was equivalent to the 0.9× labeled rate of glyphosate, whereas the putatively resistant lines exhibited a broad range of resistance with LD50 values ranging from 3.5 to 59.7× the labeled rate of glyphosate. The GR50 value for the most resistant line was 2.5-fold greater than the susceptible biotype (317 g ae ha−1 of glyphosate). These results confirm the first documented case of a glyphosate-resistant weed species in Texas.

Las especies de Amaranthus resistentes al glifosato son un riesgo reconocido en la agricultura de los Estados Unidos. Con una superficie de cultivo afectada que excede 1.2 millones de hectáreas, esta epidemia es particularmente pertinente a las regiones agrícolas que utilizan un programa intensivo de manejo basado en glifosato para el control de maleza. Antes de 2006, Texas no había identificado poblaciones resistentes al glifosato. En el condado de Wharton, Texas en 2006 y 2008 se identificaron dos poblaciones independientes de Amaranthus rudis, las cuales exhibieron poco control a la aplicación de glifosato. El objetivo de la presente investigación fue caracterizar el nivel de resistencia a glifosato (LD50 y GR50) en cada población. De esas dos poblaciones de Amaranthus rudis presumiblemente resistentes al glifosato, fueron comparados cuatro biotipos para confirmar resistencia y susceptibilidad a glifosato, en condiciones de invernadero. El valor LD50 para la población susceptible (736 g ea ha−1) fue equivalente a 0.9X la dosis recomendada de glifosato, mientras las líneas presumiblemente resistentes exhibieron un amplio rango de resistencia con valores LD50 que variaron de 3.5 a 59.7X la dosis recomendada de glifosato. El valor GR50 para las líneas más resistentes fue 2.5 veces mayor que el biotipo susceptible (317 g ea ha−1 de glifosato). Estos resultados confirman el primer caso documentado de una especie de maleza resistente a glifosato en Texas.

Weed Biology and Competition
Copyright © Weed Science Society of America 

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