Vegetable oils are considered agents rationally safe in the pest control, but they need to be emulsified correctly. This work aimed to develop a methodology to select surfactants for oils. Three substances were studied (a neutral detergent, sodium ricinoleate and a commercial spreader) in order to emulsify refined cotton oil. Their phythotoxicity in an indicative plant (melon) and miscibility of the emulsification stage were carried on. To test the miscibility the treatments were: 6.25; 12.5; 25.0; 50.0 and 75.0% of each emulsifier added to the corresponding refined cotton oil (v/v). Using the most stable percentage, the emulsifiers were used on the phythotoxicity treatments. The proportions were: 1.0; 2.0; 4.0 and 8.0% of the cotton oil formulation. Neutral detergent showed most stability at 6.25% (8 minutes); sodium ricinoleate was at 50.0% (77.75 minutes), and commercial spreader at 25.0% (32.75 minutes). Phytotoxicity was observed only with sodium ricinoleate and commercial spreader at 8.0% cotton oil. The phytotoxicity doesn’t just depend on intrinsic factors of each oil, but also on the surfactant used.
