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Fall armyworm, <i>Spodoptera frugiperda</i> (JE Smith) (Lepidoptera: Noctuidae), is a destructive pest of a wide array of agricultural and horticultural crops worldwide. This in vitro research assessed the combined effect of methanolic extracts of indigenous flora of Soone Valley (Khushab, Pakistan) and nine commonly used synthetic insecticides against 3rd instar larvae of <i>S. frugiperda</i> using the leaf-dip bioassay method. Toxicity bioassays with twelve plant extracts revealed that the extracts of <i>Withania somnifera</i> (L.) Dunal, <i>Sophora mollis</i> (Royle) Baker and <i>Rhazya stricta</i> Decne. were the most effective, exhibiting minimum LC₅₀ and LT₅₀ values. Bioassays with synthetic insecticides revealed a significantly higher mortality of <i>S. frugiperda</i> larvae by emamectin benzoate (45%), chlorpyrifos (40%) and chlorantraniliprole (38%). Further bioassays with 10 binary combinations of these most effective botanical and synthetic insecticides showed that seven pesticidal combinations exhibited synergistic toxicity, and three combinations comprising emamectin benzoate exhibited an additive effect on the mortality of <i>S. frugiperda</i> larvae. GC–MS analyses of methanolic extracts of <i>W. somnifera</i>, <i>S. mollis</i> and <i>R. stricta</i> revealed 1,2,4-trimethyl-benzene and 3,5-dimethyl-octane, 1-ethyl-2-methyl-benzene, and 1-monolinoleoylglycerol trimethylsilyl ether, decane, and lupeol as major bioconstituents, respectively. Our results demonstrated that combining botanicals with synthetic insecticides can synergize their toxicity against <i>S. frugiperda</i> larvae, suggesting their potential incorporation into future IPM programs against <i>S. frugiperda</i> and other lepidopterous pests.