ORIGINAL ABSTRACT

BACKGROUND: Bio-based quaternary ammonium salts derived from glycine betaine represent a promising class of surface-active herbicides with potential applications in sustainable crop protection. However, their phytotoxic behavior, selectivity, and environmental availability remain insufficiently understood. This study aimed to evaluate the herbicidal potential of alkyl betainate bromides with different alkyl chain lengths (C6-C16) and to determine how molecular structure, exposure route, and plant species influence biological activity. RESULTS: Soil-free assays revealed strong phytotoxicity of intermediate-chain homologs, whereas soil-based experiments showed reduced activity, indicating that environmental interactions, including limited bioavailability, influence efficacy. Greenhouse foliar applications demonstrated clear dose- and species-dependent responses. The C10 derivative showed the highest activity, causing 81-86% biomass reduction and 65-70% visual injury in Brassica napus at 1-2 kg ha-1, with efficacy comparable with the reference herbicides glyphosate (92%) and mesotrione (90%). By contrast, Triticum aestivum and Sorghum bicolor exhibited high tolerance at comparable doses, indicating a distinct selectivity window. At 10 kg ha-1, C10 and C12 caused 97% and 81% biomass reduction in B. napus, respectively; growth inhibition in monocotyledonous crops remained below 26%. CONCLUSION: The results demonstrate that glycine betaine-derived esterquats are not broad-spectrum herbicides but selective bioactive compounds with potential for targeted post-emergence weed management. Their activity depends on an optimal balance between hydrophobicity, surface activity, bioavailability, and plant-specific responses. These compounds may serve as multifunctional additives to agrochemical ingredients or complementary tools in selective weed management strategies, particularly where species-specific activity and contact-type phytotoxicity are desirable. © 2026 Society of Chemical Industry.