Managing Herbicide-Resistant Palmer Amaranth (Amaranthus palmeri) from West Tennessee with Sequential Applications of Dicamba with and without Glufosinate

Palmer amaranth has become one of the most problematic weeds in row crop production in the Midsouth. With increasing resistance to multiple herbicides, new control methods are needed. Field experiments were conducted in 2024 and 2025 at four locations in West Tennessee to evaluate the efficacy of dicamba and glufosinate applied alone, tank-mixed, or sequentially using a split-boom approach for controlling auxin herbicide-resistant Palmer amaranth populations. Control varied widely among populations, reflecting differences in dicamba resistance levels. Populations with low dicamba resistance treated with glufosinate showed 99% control following sequential applications, with no differences between tank-mix and split-boom methods. In contrast, populations with high dicamba resistance demonstrated reduced control across all treatments; however, the split-boom application improved initial control at one highly-resistant site compared with the tank-mixed application. Sequential applications improved control at all locations compared with the initial application. Increasing the spray carrier volume from 140 to 280 L ha-1; did not improve control of Palmer amaranth. These results indicate that sequential applications of dicamba plus glufosinate are required to maximize control of auxin-resistant Palmer amaranth, but efficacy is population dependent, underscoring the need for crop scouting and integrated weed management strategies to mitigate resistance development to sustain herbicide effectiveness.