Utilizing Glyphosate- and Dicamba-Tolerant Soybeans in a Wheat and Hairy Vetch Cover Crop Combination for Controlling Palmer amaranth
Montogmery, G. B., M. A. McClure, R. M. Hayes, F. R. Walker, S. A. Senseman, and L. E. Steckel.  2017.  Weed Science.

Abstract:
A study was conducted to evaluate the response of glyphosate- and dicamba-resistant (GDR) soybeans and weed control from different termination intervals before and after soybean planting into a wheat + hairy vetch cover crop. Cover crop biomass was highest when terminated at planting, and decreased with the 7 DPP and 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. However, treatments receiving a POST application of glyphosate + dicamba yielded 100 kg ha-1 higher than those treated with fomesafen. Palmer amaranth control at the 21 and 28 DAT was 97 to 99%, with dicamba providing the greater control at these ratings. Differences in Palmer amaranth control were not detected among herbicide programs or termination intervals at the final rating (R6 soybean growth stage) 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 termination delayed 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 MOA to maximize Palmer amaranth control and soybean yields.