|EUBANK, THOMAS - Delta Research & Extension Center|
|POSTON, DANIEL - Pioneer Hi-Bred International|
|SHAW, DAVID - Mississippi State University|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2012
Publication Date: 12/19/2012
Citation: Eubank, T.W., Nandula, V.K., Poston, D.H., Shaw, D. 2012. Multiple resistance of horseweed to glyphosate and paraquat and its control with paraquat and metribuzin combinations. Agronomy Journal. 2:358-370.
Interpretive Summary: Horseweed, the first broadleaf weed documented to be resistant to glyphosate, has spread across several states of the United States including Mississippi. A glyphosate resistant horseweed population in Washington County of Mississippi was suspected to be resistant to paraquat as well, thereby, severely limiting available management options. Scientists from Mississippi State University, the Crop Production Systems Research Unit (USDA-ARS), and other institutions conducted studies to verify and quantify resistance to paraquat in a glyphosate-resistant horseweed population and determine feasibility of horseweed control with paraquat and metribuzin tank mixtures. The level of glyphosate resistance in the resistant horseweed population was 12-fold compared with a susceptible population. The level of paraquat resistance in the glyphosate-resistant horseweed population was 9-fold compared to the susceptible population. The addition of metribuzin to paraquat improved horseweed control. The above results provide evidence of a looming problem of resistance in horseweed to two differently acting herbicides, glyphosate and paraquat, and of an effective horseweed control strategy that involves application of paraquat in combination with metribuzin.
Technical Abstract: Greenhouse and field studies were conducted in 2007 and 2008 to investigate possible multiple-resistance of horseweed to paraquat and glyphosate, and to evaluate the effect of the addition of metribuzin to paraquat on control of paraquat-resistant horseweed. Results indicated that the GR50 (herbicide dose required to cause a 50% reduction in plant growth) value for the susceptible population (S102) was 0.066 kg ae/ha glyphosate, and for the resistant population (MDOT) was 0.78 kg/ha glyphosate. The level of glyphosate resistance for MDOT was 12-fold compared with S102. The GR50 value for S102 was 0.078 kg ai/ha paraquat, and for MDOT was 0.67 kg/ha paraquat. The level of paraquat resistance for MDOT was 9-fold compared to S102, suggesting multiple-resistance to glyphosate and paraquat in the MDOT population. The addition of metribuzin to paraquat improved horseweed control.