Response surface optimization of imazethapyr dose and application timing for weed suppression and faba bean yield

Effective weed management in faba bean (Vicia faba L.) requires precise adjustment of herbicide dose and application timing to achieve effective weed suppression while maintaining crop growth and yield. This study employed response surface methodology (RSM) to quantify and optimize the interactive effects of imazethapyr rate and application timing on weed biomass, morphophysiological traits, and yield of faba bean under field conditions in western Iran during a single 2024-2025 growing season.Imazethapyr (Pursuit^® 10% SL) was applied at rates ranging from 0 to 1000 mL ha⁻¹ at pre-plant incorporated, pre-emergence, and post-emergence stages using a central composite design. Leaf area index, plant height, number of pods per plant, 100-seed weight, biological yield, grain yield, and weed dry weight were modeled using quadratic and cubic RSM functions. Strong nonlinear dose by timing interactions were observed for all responses. Intermediate imazethapyr rates (250-500 mL ha⁻¹) applied from pre-planting to early post-emergence (3-10 days after sowing) maximized canopy development, reproductive performance, biological yield, and grain yield while minimizing weed biomass. Higher rates (≥ 750 mL ha⁻¹) or late post-emergence applications reduced crop performance despite improved weed suppression, indicating phytotoxic effects. Model diagnostics showed high predictive accuracy, particularly for leaf area index, 100-seed weight, and weed dry weight. Multi-response desirability analysis identified a favorable management range balancing weed control and yield performance, indicating the value of RSM as a decision-support framework for precision herbicide management in faba bean.