Two Sumithion® formulations were sprayed aerially to compare their effectiveness in controlling spruce budworm, Choristoneura fumiferana (Clemens), in balsam fir, Abies balsamea (L.) Mill. Sumithion 20% flowable, a new formulation, and Sumithion technical were applied twice at 210 g AI (in 1.5 L of spray mix)/ha using a Cessna 188 Agtruck equipped with four Micronair atomizers. More than 95% of the technical and <45% of the Sumithion flowable spray droplets were <50 μm in diameter. Larval reduction ranged from 67 to 84% in the Sumithion flowable plots, from 52 to 55% in the Sumithion technical plots, and from 28 to 38% in the untreated plots. Postspray residual populations averaged 4.1, 6.2, and 10.3 larvae per 46-cm branch in the flowable, technical, and untreated blocks, respectively. Defoliation in the Sumithion flowable block averaged 18.5% and was not significantly different from the technical block but both were significantly less (α = 0.05) than that in the untreated block, which averaged 46.2%. The results suggest that Sumithion 20% flowable was more efficacious in controlling spruce budworm than Sumithion technical insecticide.