The tobacco cutworm, Spodoptera litura(Fabricius), is a major pest of tomato and frequently demands control measures. The timing of insecticide application is a key factor in determining its efficiency, so an experiment was designed to investigate this. Application of insecticide was based on three criteria: (i) the number of trap-caught moths in a Delta-type trap with a commercial sex pheromone lure placed in the center of the target area, soon after plant emergence; (ii) the percentage of plants exhibiting pinhole-type damage (10% or 20%) and (iii) the percentage of plants exhibiting shot hole-type damage (10% or 20%) compared to a check plot without any control measures. We found that the number of trap-caught moths was, compared to the other methods, the best means of deciding on insecticide application in tomato plant to control the tobacco cutworm. Using pheromone traps, we obtained the best performance of the insecticide Shinnago, causing > 90% larval mortality. Without insecticide application, tomato yield reduction due to the tobacco cutworm larva damage was 27%.