Safety Evaluation of Cyhalofop-Butyl on Agronomic Traits and Antioxidant Enzyme Activities in Foxtail Millet

Weed infestation severely impairs foxtail millet growth, while new herbicide development faces long cycles and high costs. This study examined cyhalofop-butyl (effective against Echinochloa crus-galli (E. crus-galli) in paddy fields) to assess its effects on agronomic traits, antioxidant enzyme activities, malondialdehyde (MDA) content of Jingu 21, and weed control efficacy in foxtail millet fields, aiming to screen safe, effective concentrations. Results showed that sole cyhalofop-butyl inhibited foxtail millet growth: high-dose treatments retained significant agronomic trait inhibition 30 days post-spray. Early post-spray, superoxide dismutase (SOD) and peroxidase (POD) activities showed a “first increase then decrease” pattern, catalase (CAT) a “first decrease then increase” trend, and MDA content rose; index differences from the water control narrowed over time, though 90 g a.i./hm2 still caused higher leaf SOD activity and MDA content in later stages. For weed control, cyhalofop-butyl effectively controlled E. crus-galli (control effect “first increase then decrease,” 90 g a.i./hm2 optimal) and Digitaria sanguinalis (D. sanguinalis) (control effect rising over time) in foxtail millet fields. On the whole, 22.5 g a.i./hm2 and 45 g a.i./hm2 of cyhalofop-butyl are safe for Jingu 21, and 67.5 g a.i./hm2 is also a safe concentration, so 45–67.5 g a.i./hm2 can be preferred for comprehensive weed control.