Managing Auxin-Resistant Palmer Amaranth ( Amaranthus palmeri ) from West Tennessee with Sequential Applications of 2,4-D with and without Glufosinate

Abstract

Auxinic herbicides (Group 4) are a crucial tool for maintaining effective weed management in modern agronomic systems. Palmer amaranth has evolved resistance to multiple herbicides, including auxinic herbicides. With documentation of auxin resistance in Palmer amaranth, new strategies should be implemented to improve management. Field studies were conducted in Tennessee during the summers of 2024 and 2025 to evaluate the efficacy of different herbicide application methods for managing auxin-resistant Palmer amaranth. The research compared tank-mixed applications of 2,4-D and glufosinate with split-applied (split-boom; herbicides applied simultaneously through separate spray booms as independent solutions) applications across multiple Palmer amaranth populations. Results demonstrated that in populations exhibiting high auxinic resistance, the split-boom application method was more effective than the conventional tank-mix approach. However, control levels were still below those typically considered acceptable for effective Palmer amaranth contol. Sequential split-boom applications were required to achieve acceptable levels of control in these populations. A second study evaluated whether carrier volume influenced the performance of these applications by comparing mixtures of 140 L ha ^-1 and 280 L ha ^-1 . The results indicated that carrier volume did not significantly affect Palmer amaranth control at these volumes.