The evolution of glyphosate and acetolactate synthase (ALS) inhibitor-resistant common waterhemp in the Midwestern United States has reduced the number of effective POST herbicide options for management of this problem weed in glyphosate-resistant soybean. Moreover, common waterhemp emerges throughout the crop growing season, justifying the need to evaluate herbicide programs that provide season-long control. The objectives of this study were to compare POST-only and PRE followed by (fb) POST herbicide programs for control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Field experiments were conducted in 2013 and 2014 in Dodge County, NE, in a field infested with glyphosate-resistant common waterhemp. Programs containing PRE herbicides resulted in ≥83% control of common waterhemp and densities of ≤35 plantsm-2 at 21 d after PRE (DAPRE). Post-only herbicide programs resulted in <70% control and densities of 107 to 215 plants m-2 at 14 d after early-POST (DAEPOST) treatment. PRE fb POST herbicide programs, including saflufenacil plus imazethapyr plus dimethenamid-P, sulfentrazone plus cloransulam, or S-metolachlor plus metribuzin, fb fomesafen plus glyphosate; S-metolachlor plus fomesafen fb acifluorfen plus glyphosate resulted in >90% control of glyphosate-resistant common waterhemp throughout the growing season, reduced density to ≤7plantsm-2, ≥92% biomass reduction, and soybean yield >2,200kg ha-1. Averaged across herbicide programs, common waterhemp control was 84%, and density was 15 plants m-2 with PRE fb POST herbicide programs compared with 42% control, and density of 101 plants m-2 with POST-only herbicide programs at harvest. Results of this study indicated that PRE fb POST herbicide programs with effective modes of action exist for season-long control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Nomenclature: Acetochlor; acifluorfen; chlorimuron-ethyl; cloransulam-methyl; dimethenamid-P; flumioxazin; fomesafen; glyphosate; imazethapyr; lactofen; saflufenacil; S-metolachlor; sulfentrazone; thifensulfuron-methyl; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr.
Bibliographical noteFunding Information:
Acknowledgments The authors would like to thank the Indian Council of Agricultural Research (ICAR), New Delhi, India for partial financial support to the graduate student involved in this study. We appreciate the help of Jordan Moody, Luke Baldridge, Ethann Barnes, Ian Rogers, Irvin Schleufer, and Mason Adams in this project.
© Weed Science Society of America, 2017 .
- Biomass reduction
- PRE followed by POST
- Resistance management
- Soybean yield