Cloransulam-methyl combined with imazapic for effective control of Cyperus rotundus and their safety in alfalfa

To clarify the feasibility of cloransulam-methyl and imazapic in alfalfa fields, their control efficacy on Cyperus rotundus and safety to alfalfa were investigated in greenhouse and field conditions. The greenhouse experiments showed that the combination of cloransulam-methyl and imazapic had a good control effect on C. rotundus. For the ratios of active ingredient dosage from 1 ꞉ 2 to 1 ꞉ 4, the co-toxicity coefficient on the plant height and fresh weight of C. rotundus ranged from 131.54 to 150.46 and 152.84 to 180.25, respectively, exhibiting a distinct synergistic effect. Among the tested combinations, synergy was the most for the 1 ꞉ 3 ratio, and the selectivity indexes of plant height and fresh weight between alfalfa and C. rotundus were 1.86 and 1.56, respectively. The field test results showed that the effectiveness of treatments ratios of cloransulam-methyl and imazapic (17.50 + 52.50)～(25.00 + 75.00) g·ha⁻¹ on alfalfa plants in Zhengzhou and Lankao were 78.5%～88.5% and 82.1%～90.8%, respectively, and 83.4%～92.7% and 84.7%～93.6% for fresh weight, respectively, with yield increase rates of 28.8%～35.1% and 30.5%～38.3%, respectively, which were significantly higher than those of cloransulam-methyl or imazapic alone. These results help address the challenge of drug damage by cloransulam-methyl and imazapic alone. The combination of imazapic and cloransulam-methyl can thus effectively prevent and control C. rotundus with improved safety to alfalfa and has good prospects for promotion and application.