BORON NUTRITION AND HERBICIDE STRATEGIES IN MANAGING GLYPHOSATE-RESISTANT PALMER AMARANTH IN Roundup ReadyÒ ALFALFA

Abstract

Alfalfa (Medicago sativa L.) is one of the most economically valuable forage crops worldwide, due to its high nutritive value and adaptability to diverse climates. However, its agronomic potential depends on proper soil fertility and weed control. Alfalfa production requires substantial inputs of macronutrients and boron, which is often the only micronutrient routinely recommended, yet often overlooked. Boron deficiency is common on coarse-textured, high-pH soils and under dry conditions, reducing regrowth vigor, stand persistence, and the crop’s ability to compete with weeds. The adoption of Roundup Ready® (RR) alfalfa initially simplified weed control, but repeated glyphosate use on resistant crops has selected for resistant weed biotypes, such as glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Watson). Alternative herbicidal options, including PPO inhibitors and paraquat, can provide effective Palmer amaranth control but are constrained by crop safety, application timing, environmental conditions, or regulatory concerns. This review aimed to consolidate existing research on boron fertility, herbicide options, and Palmer amaranth biology to clarify how these factors are related, and to guide integrated management strategies for productive and more sustainable alfalfa systems Keywords: weed control; hay; legume; herbicide; resistance.