Response of Nebraska Kochia (Kochia scoparia) Accessions to Dicamba

Weed Technology 28(1):151-162. 2014

Roberto J. Crespo, Mark L. Bernards, Gustavo M. Sbatella, Greg R. Kruger, Don J. Lee, and Robert G. Wilson

First, second, and fifth authors: Graduate Research Assistant, Assistant Professor, and Professor, respectively Department of Agronomy and Horticulture, University of Nebraska–Lincoln, Lincoln, NE 68583; third author: Assistant Professor, Central Oregon Agricultural Research Center, Oregon State University, Madras, OR 97741; fourth author: Assistant Professor, West Central Research and Extension Center, University of Nebraska–Lincoln, North Platte, NE 69101; sixth author: Professor, Panhandle Research and Extension Center, University of Nebraska–Lincoln, Scottsbluff, NE 69361. Current address of second author: School of Agriculture, Western Illinois University, Macomb, IL 61455.

Corresponding author's E-mail: rojacre@yahoo.com.ar

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.