Resistance status of Alopecurus aequalis to commonly used ACCase inhibitors in some rice-wheat rotation areas of Anhui Province and screening of mixed formula of post-emergence herbicides

In order to clarify the resistance status of Alopecurus aequalis to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides, 30 populations of A. aequalis were collected from rice-wheat rotation fields in Anhui Province and determined by whole plant bioassay of resistance levels to three ACCase herbicides, including fenoxaprop-P-ethyl, clodinafop-propargyl and pinoxaden. Seven kinds of post-emergence herbicides such as tralkoxydim and pyroxsulam were selected for the boi-activity test to highly resistant population AHCZ-2. Five herbicides mixed with isoproturon were employed for the field efficacy evaluation. The results showed that among 30 tested populations, 26 populations were highly resistant to fenoxaprop-P-ethyl, accounting for 86.67% of the total tested populations. The GR₅₀ value (active ingredients, the same as below) was 230.93-1755.54 g/hm², and resistance index (RI) was 12.58-95.66. Twenty-one populations were highly resistant to clodinafop-propargyl, accounting for 70% of the total tested populations. The GR₅₀ value was 147.18-1213.44 g/hm², and RI was 11.93-98.36. The 19 populations were highly resistant to pyraclostrobin, accounting for 63.33% of the total tested. The GR₅₀ value ranged from 107.63 to 614.18 g/hm², and RI ranged from 12.21 to 69.69. The resistance of A. aequalis populations collected from the same area to three kinds of ACCases inhibitors was similar. Among the 7 kinds of post-emergence herbicides tested, the activity to highly resistant A. aequalis population AHCZ-2 was higher in tralkoxydim and chlortoluron with GR₉₀ of 468.74 g/hm² and 1495.85 g/hm², followed by cypyrafluone-isoproturon with the GR₉₀ of 1035.62 g/hm². The activity of isoproturon, pyroxsulam, mesosulfuron-methyl and flucarbazone-Na was low. The field screening results showed that recommended high dose mesosulfuron-methyl (15.75 g/hm²), pyroxsulam (15 g/hm²) and chlortoluron (2250 g/hm²) mixed with isoproturon at 1500 g/hm² had the best control efficacy on A. aequalis. The plant control efficacy was between 91.18% and 94.05%, and the fresh weight control efficacy was between 92.40% and 95.68%, the yield increased by 25.04%-35.08%. Cypyrafluone-isoproturon at 937.5 g/hm² was the next with 90.78% control efficacy of fresh weight and yield increase of 22.78%. The results can provide reference for chemical control of rice-wheat field resistance A. aequalis.