Herbicide Resistance: Realities and Management

Abstract

Herbicide resistance is an increasing constraint to sustainable weed management and crop production. Repeated and continuous use of herbicides with the same mode or site of action has intensified selection pressure, favouring resistant weed populations and reducing the efficacy of widely used herbicides. This review synthesises the current status, major mechanisms and management options for herbicide resistance, with attention to both global trends and the Indian context. Globally, 548 unique cases of herbicide resistance have been documented across 275 weed species, involving resistance to 21 herbicide sites of action. In India, resistance was first documented in Phalaris minor against isoproturon in wheat and has subsequently been reported in other weed species, including Cyperus difformis and Echinochloa crus-galli in rice ecosystems. The review discusses biological, agronomic and herbicide-related factors that influence resistance development, including weed life cycle, seed production, herbicide use pattern, cropping system uniformity and selection pressure. It also outlines major resistance types, namely single resistance, cross resistance, multiple resistance and negative cross resistance. Mechanisms are considered under target-site resistance (TSR) and non-target-site resistance (NTSR). TSR includes altered herbicide-binding sites and increased target enzyme production, whereas NTSR includes reduced herbicide uptake and translocation, sequestration, compartmentation and enhanced metabolic detoxification mediated by enzymes such as cytochrome P450 monooxygenases, glutathione S-transferases and glycosyl transferases. Management requires a shift from herbicide-dependent practices to integrated weed management, including herbicide rotation and mixtures, cultural and mechanical practices, harvest weed seed control and precision weed management. Sustainable resistance management depends on diversified, preventive strategies that reduce selection pressure, preserve herbicide efficacy and support long-term agricultural productivity.