Efficacy Evaluation of Cyclobutrifluram Against Root-Knot Nematode Disease of Three Crops

Plant-parasitic nematodes are recognized as important pathogens that pose a persistent and serious threat to global agricultural production. Among them, Meloidogyne incognita is one of the most widely distributed and destructive species. Root-knot nematode disease caused by M. incognita has an impact on the yield and quality of various vegetables and economic crops such as tomato, watermelon, carrot worldwide, and thus emerging as a key soil-borne disease that seriously endangers global food security and agricultural sustainability. To explore a novel control strategy for highly efficient and sustainable prevention and control, this study systematically evaluated the laboratory toxicity of cyclobutrifluram, a novel succinate dehydrogenase inhibitor (SDHI) nematicide, against M. incognita. On this basis, standardized field efficacy tests were conducted in 2023 across different economic crop production areas of Henan Province. The 450 g/L cyclobutrifluram concentrate was applied via root-irrigation with the recommended dosage of 555 mL/hm² to verify its field control efficacy on tomato, carrot and watermelon. Laboratory toxicity assays demonstrated that cyclobutrifluram exhibited strong toxicity against the second-stage juveniles (J2) of M. incognita, with the median lethal concentration (LC50) value of 0.35 mg/L, which was significantly higher than that of fosthiazate (LC50=19.8 mg/L) and fluopyram (LC50=2.15 mg/L), providing a robust pharmacodynamic basis for its field application. Field test results showed that soil drenching with 450 g/L cyclobutrifluram concentrate at a dosage of 555 mL/hm² could significantly reduce the root-knot indices of the three crops, and the control efficacies against root-knot nematode disease of tomato, carrot and watermelon were 82.50%, 72.92% and 79.07% respectively. At the same time, it could remarkably promote the growth of crop roots and plants, reflecting the agent's dual benefits of disease control and plant growth promotion. In terms of yield performance, the yields of tomato, carrot and watermelon treated with cyclobutrifluram reached 134.55, 76.71, 40.24 t/hm², with corresponding yield increase rates of 64.11%, 55.95% and 24.12%, respectively, indicating the significant potential of cyclobutrifluram in increasing yield and income. To further explore the optimal application dosage for severely infested areas, an additional high-dosage treatment group of 1155 mL/hm² was set up with watermelon as the test crop. The results indicated that increasing the dosage could further improve the control efficacy of cyclobutrifluram against watermelon root-knot nematode disease to 86.05%, with the yield reaching 42.77 t/hm² and the yield increase rate rising to 31.92%. This finding suggests that appropriately increasing the application dosage can achieve better control effects in heavily infested fields. In conclusion, cyclobutrifluram exhibits excellent laboratory toxicity and stable field control efficacy against M. incognita, can significantly promote crop growth and yield improvement, and its dosage adjustment can meet the control requirements of fields with different infestation severities. The results of this study confirms that as a novel nematicide with a unique mode of action, high efficiency and relatively low environmental risk, cyclobutrifluram can be served as an effective alternative agent for current nematode resistance management and integrated root-knot nematode disease control, and has great value for popularization and application.