An emulsifiable concentrate of carbaryl was developed and its efficacy improved by synergization with isobornyl thiocyanoacetate. The formulations exhibited satisfactory physico-chemical characteristics. Emulsions (up to 0.2% carbaryl) from these concentrates exhibited no phytotoxicity against Vicia faba, Daucus carrota, Brassica oleracea, Gossypium hirsutum, Rabhanus sativus, Brassica juncea and Lycopersicum esculentum. The synergized concentrate, however, showed phytotoxicity against Solanum tuberosum and Hibiscus esculentus. Isobornyl thiocyanoacetate showed a factor of synergism of 2.5 at the 1:1 synergized concentrate. For a comparable bioefficacy with the commercial WDP, only 1/3 to 1/5 of carbaryl from these concentrates was required. Their 0.05% emulsions controlled the bollworm complex in cotton, increased seed cotton yield and left no detectable residues in lint and seed at harvest. In insect control and yield increase, the 0.05% emulsions from the synergized EC matched 0.2% carbaryl from WDP and 0.02% fenvalerate emulsions. Carbaryl WDP and fenvalerate, however, left detectable residues at harvest.