A study was conducted to evaluate the response of glyphosate- and dicamba-tolerant (GDT) soybean and weed control from cover crop different termination intervals before and after soybean planting. Cover crop biomass was highest when terminated at planting, decreased with the 7- and 14-d preplant (DPP) and day-after-planting (DAP) timings, and again at the 14 DPP and DAP timings. Glyphosate dicamba provided total control of cover crops by 21 DAP. Cover crop termination timing did not influence soybean population or yield. Palmer amaranth control at the 21 and 28 d after termination (DAT) was 97% to 99%. Differences in Palmer amaranth control were not detected among herbicide programs or termination intervals at the end of season rating, and all treatments provided ≥97% control. Although differences in Palmer amaranth control were not apparent at the end of the season, the delay in cover crop affected the number of days until 10-cm Palmer amaranth was present. When utilizing a wheat hairy vetch cover crop in DGT soybeans, producers should delay cover crop termination until 11 to 14 DPP and make at least one POST application of glyphosate dicamba an additional herbicide mode of action (MOA) to maximize Palmer amaranth control and soybean yields.
Nomenclature: Glyphosate; dicamba; fomesafen; Palmer amaranth, Amaranthus palmeri (S.) Wats.; hairy vetch, Vicia villosa Roth.; wheat, Triticum aestivum L.; soybean, Glycine max (L.) Merr.