A Binary Mixture of Emamectin Benzoate and Chlorantraniliprole Supplemented with an Adjuvant Effectively Controls Spodoptera frugiperda

SIMPLE SUMMARY: The fall armyworm (FAW) Spodoptera frugiperda causes severe crop loss worldwide, urging effective prevention and control strategies. This study selects an effective binary mixture of emamectin benzoate and chlorantraniliprole at a mass ratio of 9:1. An oil-based adjuvant reduces the dose of the binary mixture by 80% in a field trial. This provides an effective insecticide–adjuvant mixture to control FAW. ABSTRACT: The fall armyworm (FAW) Spodoptera frugiperda is a notorious pest, causing severe crop damage worldwide and prompting effective prevention and control. Over-reliance on and intensive use of insecticides are prone to leading to the rapid evolution of insecticide resistance, urging rational insecticide application. One effective way of rational insecticide application is to apply insecticides of different modes of action in combination or supplemented with adjuvants. In this study, we assessed the efficacies of two individual insecticides, emamectin benzoate (EB) and chlorantraniliprole (CT), and their mixture, supplemented with and without the oil adjuvant Jijian(®) to control FAW in laboratory bioassays and a field trial. Both EB and CT showed high toxicities to FAW. The EB × CT mixture at a mass ratio of 9:1 yielded a remarkable synergistic effect, with the co-toxicity coefficient (CTC) being 239.38 and the median lethal concentration (LC50) being 0.177 mg/L. In leaf-spray bioassays, the addition of the adjuvant reduced the LC50 values of both the individual insecticides and the EB × CT mixture by more than 59%, significantly improving the efficacies. The field trial confirmed the synergistic effects of the adjuvant, which reduced the amount of EB × CT mixture by 80%. This study provides an effective and promising insecticide–adjuvant mixture to control S. frugiperda.