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1 January 2014 Influence of Application Timing and Glyphosate Tank-Mix Combinations on the Survival of Glyphosate-Resistant Giant Ragweed ( Ambrosia trifida) in Soybean
Eric B. Riley, Kevin W. Bradley
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Abstract

In recent years, glyphosate-resistant (GR) giant ragweed has become an increasingly problematic weed in soybean in Missouri and throughout many areas of the Midwest. Field trials were conducted in 2010 and 2011 to determine the influence of various application timings and glyphosate tank-mix combinations on the survival of GR giant ragweed in soybean. Glyphosate was applied alone and in combination with selected tank-mix combinations early POST (EPOST) to 10-, 20-, or 30-cm GR giant ragweed. Treatments received late POST (LPOST) applications approximately 3 wk after EPOST applications, once GR giant ragweed resumed growth. GR giant ragweed survival 2 wk after EPOST applications (2 WAEPOST) ranged from 60 to 100%. Glyphosate plus fomesafen applications to 10-cm plants resulted in 60% survival of GR giant ragweed, which was the lowest survival observed across all treatments and application timings. However, GR giant ragweed survival ranged from 37 to 98% 4 wk after LPOST applications (4 WALPOST). Glyphosate plus fomesafen applications to 10-cm plants resulted in 37% survival of GR giant ragweed 4 WALPOST, which was the lowest survival observed across all treatments and application timings. Few differences in soybean yields were observed between herbicide treatments within application timings in either year, and all herbicide treatments resulted in yields higher than the nontreated control. In 2011, soybean yields were reduced following glyphosate tank-mix combinations to larger plants. Overall, higher soybean injury and GR giant ragweed survival was observed in response to glyphosate tank-mix combinations made to taller plants. Results from this research indicate that additional methods of GR giant ragweed control, other than POST-only glyphosate tank-mix combinations, will be needed for effective management of GR giant ragweed in GR soybean.

Nomenclature: Glyphosate; giant ragweed; Ambrosia trifida L; soybean; Glycine max (L.) Merr.

En años recientes, Ambrosia trifida resistente a glyphosate (GR) se ha convertido en una maleza problemática en soya en Missouri y en muchas áreas del Medio Oeste de los Estados Unidos. En 2010 y 2011 se realizaron estudios de campo para determinar la influencia de varios momentos de aplicación y combinaciones de mezclas en tanque con glyphosate sobre la supervivencia de A. trifida GR en soya. Se aplicó glyphosate solo y en combinación en mezclas en tanque con herbicidas selectos en POST temprana (EPOST) a A. trifida GR de 10, 20, ó 30 cm. Los tratamientos recibieron aplicaciones POST tardías (LPOST) aproximadamente 3 semanas después de las aplicaciones EPOST, una vez que A. trifida GR reiniciaron el crecimiento. La supervivencia de A. trifida GR 2 semanas después de las aplicaciones EPOST (2 WAEPOST) variaron de 60 a 100%. Aplicaciones de glyphosate más fomesafen a plantas de 10 cm resultó en una supervivencia de A. trifida GR de 60%, la cual fue la menor supervivencia observada en todos los tratamientos y momentos de aplicación. Sin embargo, la supervivencia de A. trifida GR varió entre 37 y 98% 4 semanas después de aplicaciones LPOST (4 WALPOST). Aplicaciones de glyphosate más fomesafen a plantas de 10 cm resultaron en una supervivencia del 37% de A. trifida GR 4 WALPOST, la cual fue la menor supervivencia observada en todos los tratamientos y momentos de aplicación. Se observaron pocas diferencias en el rendimiento de la soya entre los tratamientos de herbicidas y momentos de aplicación en cada año, y todos los tr

Eric B. Riley and Kevin W. Bradley "Influence of Application Timing and Glyphosate Tank-Mix Combinations on the Survival of Glyphosate-Resistant Giant Ragweed ( Ambrosia trifida) in Soybean," Weed Technology 28(1), 1-9, (1 January 2014). https://doi.org/10.1614/WT-D-13-00098.1
Received: 31 May 2013; Accepted: 1 August 2013; Published: 1 January 2014
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KEYWORDS
Application timing
glyphosate resistant
glyphosate tank-mix combinations
glyphosate-resistant soybean
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