This study aims to evaluate the allelopathic potential of Brassica juncea (YR_ab2) against dominant invasive weeds in agricultural systems, thereby providing a scientific foundation for the green and sustainable management of invasive weed species. This study employed the Petri dish filter paper method to assess the allelopathic effects of root exudates from Brassica juncea (YR_ab2) on seed germination and seedling growth of four invasive weed species: Phalaris minor, Avena fatua, Galinsoga parviflora, and Ageratum conyzoides. The allelopathic index (RI), comprehensive allelopathic effect (SE), and toxicity (LC₅₀) values, were quantitatively evaluated. The results showed that within the concentration range of 5 to 80 mL/plant, the root exudates of Brassica juncea (YR_ab2) significantly inhibited seed germination and seedling growth of the four invasive weed species. The allelopathic response, assessed through the relative inhibition index (RI), showed negative values across all measured parameters, including germination rate (RI: -0.621 to -0.008), germination index (RI: -0.844 to -0.039), root length (RI: -0.865 to -0.056), shoot length (RI: -0.824 to -0.021), and biomass (RI: -0.734 to -0.063), indicating consistent inhibitory effects. The comprehensive allelopathic effect (SE) also remained negative (range: -0.761 to -0.040). Notably, the magnitude of inhibition increased with decreasing concentration, suggesting a non-monotonic dose-response relationship. At concentrations of 5, 10, 20, and 40 mL/plant, all parameters were significantly suppressed compared to the control (P<0.05), with the strongest inhibition observed at the lowest tested concentration (5 mL/plant). These results demonstrate that Brassica juncea (YR_ab2) root exudates exert a potent allelopathic inhibitory effect on both seed germination and early seedling development of the target weeds. Toxicity analysis revealed that the root exudates of v Brassica juncea (YR_ab2) exhibited differential inhibitory effects on seed germination and seedling growth across the four invasive weed species. The lowest LC₅₀ values, indicative of higher phytotoxicity, were observed for Galinsoga parviflora seed germination (LC₅₀: 8.023 mL/plant for germination rate; 19.979 mL/plant for germination index) and Ageratum conyzoides seedling growth (LC₅₀: 21.292 mL/plant for root length; 20.316 mL/plant for shoot length), suggesting greater sensitivity of these species to the exudates compared to others. In contrast, Avena fatua displayed the highest LC₅₀ values, indicating the lowest susceptibility to both germination and growth inhibition. These findings demonstrate that, under equivalent concentrations of root exudate application, Galinsoga parviflora and Ageratum conyzoides experience more pronounced inhibitory effects, particularly in early developmental stages. The root exudates of Brassica juncea (YR_ab2) exhibit strong allelopathic inhibitory potential against both seed germination and seedling growth of four invasive weed species. Notably, they show pronounced phytotoxic effects on Galinsoga parviflora and Ageratum conyzoides, highlighting their promise for application in ecological weed management and sustainable, non-chemical control strategies. These findings provide a scientific foundation for the green and environmentally sustainable governance of invasive weeds in agricultural systems.