Integrating a cereal rye cover crop and soybean row width with herbicides to manage Palmer amaranth in Michigan

"Glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) is an emerging concern for Michigan farmers. Integrating the use of cultural practices such as cover crops and narrow soybean row width may improve the control of herbicide-resistant Palmer amaranth in Michigan. In 2015 and 2016, field experiments investigated the effects of a cereal rye cover crop, including termination method, and soybean row width as cultural practices to improve Palmer amaranth control with herbicides. Additional pot experiments were conducted to evaluate the effects of cereal rye stage, biomass, and termination method on Palmer amaranth emergence. Cereal rye biomass was greater in 2016 compared with 2015 due to the greater accumulation of growing degree days prior to cereal rye termination. Winter annual weeds were suppressed by more than 75% with cereal rye. However, overall Palmer amaranth emergence and control was not effected by cereal rye. In outdoor pot experiments, cereal rye suppression of Palmer amaranth emergence varied by year with the most consistent suppression with the later stage (Feekes 10.1 or later) cereal rye. In greenhouse pot experiments, total Palmer amaranth emergence was only reduced by cereal rye terminated by cutting compared with chemical termination. Planting soybean in narrow rows reduced the emergence period of Palmer amaranth in both years. Palmer amaranth was effectively controlled by both herbicide management strategies in 2015, while only the high management strategy provided season-long control in 2016. Utilizing an intensive herbicide management program and planting soybean in narrow rows provided the greatest impact on Palmer amaranth management in Michigan soybean production."--Page ii.