Evaluation of the indoor activity and field efficacy of 4-methoxy-2-nitrophenyl 2,6-bis((4,6-dimethoxypyrimidin-2-yl)oxy) benzoate on several weeds in field

2-(Pyrimidin-2-yloxy)benzoic acid (PYB) herbicides are known for their rapid degradation in soil and lack of phytotoxicity to subsequent crops. Building on our previous work with bispyribac-sodium as the lead compound, the group synthesized and screened a highly active candidate compound, (2-nitro-4-methoxy)phenyl(2,6-(4,6-dimethoxy)pyrimidine-2-oxy)benzoate (Ia-19), which targets acetolactate synthase (ALS). To evaluate the application potential of Ia-19, the herbicidal activity of a 10% oil-based suspension concentrate (OD) of Ia-19 through both pot and field experiments was assessed, focusing on its efficacy against weeds and its impact on the growth and yield of direct-seeded rice. In the indoor herbicidal activity test, the fresh weight inhibition rates of 10% Ia-19 OD against barnyard grass, Galium spurium L., and other major field weeds exceeded 80% at application rates of 45, 60, and 90 g a.i./hm², demonstrating comparable efficacy to 10% bispyribac-sodium OD at the same dosages. In the field control experiment, the efficacy of weed control at application rates of 60 and 90 g a.i./hm² exceeds 60% in terms of weed population reduction after 15 days. However, the control efficacy observed 30 days post-application was significantly lower than that at 15 days, suggesting the germination of new weeds. Notably, by day 30, the control efficacy of all three experimental concentrations of Ia-19 on weed fresh weight remained relatively high, although its overall performance was slightly inferior to that of bispyribac-sodium. Yield determination results indicated that rice fields treated with 90 g a.i./hm² of 10% Ia-19 OD exhibited a 22.35% increase in yield compared to untreated fields. No significant phytotoxicity observed even at this higher dosage, suggesting that Ia-19 is a safe herbicide candidate for rice.