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1 January 2014 Response of Nebraska Kochia ( Kochia scoparia) Accessions to Dicamba
Roberto J. Crespo, Mark L. Bernards, Gustavo M. Sbatella, Greg R. Kruger, Don J. Lee, Robert G. Wilson
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Abstract

Kochia is a troublesome weed in the western Great Plains and many accessions have evolved resistance to one or more herbicides. Dicamba-resistant soybean is being developed to provide an additional herbicide mechanism of action for POST weed control in soybean. The objective of this study was to evaluate variation in response to dicamba among kochia accessions collected from across Nebraska. Kochia plants were grown in a greenhouse and treated when they were 8 to 12 cm tall. A discriminating experiment with a single dose of 420 g ae ha−1 of dicamba was conducted on 67 accessions collected in Nebraska in 2010. Visual injury estimates were recorded at 21 d after treatment (DAT) and accessions were ranked from least to most susceptible. Four accessions representing two of the most and least susceptible accessions from this screening were subjected to dose-response experiments using dicamba. At 28 DAT, visible injury estimates were made and plants were harvested to determine dry weight. An 18-fold difference in dicamba dose was necessary to achieve 90% injury (I90) between the least (accession 11) and most susceptible accessions. Approximately 3,500 g ha−1 of dicamba was required in accession 11 to reach a 50% dry weight reduction (GR50). There was less than twofold variation among the three more susceptible accessions for both the I90 and GR90 parameters, suggesting that most kochia accessions will be similarly susceptible to dicamba. At 110 DAT, accession 11 had plants that survived doses of 35,840 g ha−1, and produced seed at doses of 17,420 g ha−1. The identification of one resistant accession among the 67 accessions screened, and the fact that dicamba doses greater than 560 g ha−1 were required to achieve GR80 for all accessions suggest that repeated use of dicamba for weed control in fields where kochia is present may quickly result in the evolution of dicamba-resistant kochia populations.

Nomenclature: Dicamba; kochia; Kochia scoparia (L.) Schrad. KCHSC; soybean; Glycine max L. Merr. GLYMX.

Kochia scoparia es una maleza problemática en el oeste de las Grandes Planicies y muchas accesiones han evolucionado resistencia a uno o más herbicidas. Se está desarrollando soya resistente a dicamba para proveer un mecanismo de acción adicional para el control de malezas POST en soya. El objetivo de este estudio fue evaluar la variación en la respuesta a dicamba entre accesiones de K. scoparia colectada a lo largo de Nebraska. Plantas de K. scoparia fueron crecidas en un invernadero y tratadas cuando tuvieron 8 a 12 cm de altura. Se realizó un experimento de discriminación con una sola dosis de 420 g ae ha−1 de dicamba con 67 accesiones colectadas en Nebraska en 2010. Estimaciones visuales de daño se realizaron 21 días después del tratamiento (DAT) y las accesiones fueron ordenadas de menor a mayor susceptibilidad. Cuatro accesiones representando dos de las accesiones más y menos susceptibles en la evaluación fueron sometidos a experimentos de respuesta a dosis usando dicamba. A 28 DAT, se realizaron las estimaciones visuales de daño y las plantas fueron cosechadas para determinar su peso seco. Una diferencia de 18 veces en la dosis de dicamba fue necesaria para alcanzar 90% de daño (I90) entre la accesión menos susceptible (accesión 11) y las más susceptibles. Se necesitó aproximadamente 3,500 g ha−1 de dicamba para reducir en 50% el peso seco (GR50) de la accesión 11. Hubo una variación de menos de dos veces en los valores de los parámetros I90 y GR90 entre las tres accesiones

Roberto J. Crespo, Mark L. Bernards, Gustavo M. Sbatella, Greg R. Kruger, Don J. Lee, and Robert G. Wilson "Response of Nebraska Kochia ( Kochia scoparia) Accessions to Dicamba," Weed Technology 28(1), 151-162, (1 January 2014). https://doi.org/10.1614/WT-D-13-00109.1
Received: 25 June 2013; Accepted: 1 October 2013; Published: 1 January 2014
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