We have developed a simulation model for decision making in management of Heliothis on cotton. Called DEMHELIC, the model uses scouting data on insect densities and on the state of the crop, and it recommends the control to use by comparing economic returns of the available options. The model has structures for cotton crop growth, Heliothis feeding, impact of beneficial insects on Heliothis feeding and survival, insecticidal mortality of Heliothis and beneficials, and economics of pest control. Maturity and temperature drive crop growth. Age of larvae, relative abundance of fruiting forms, and temperature drive feeding rate of Heliothis, and temperature drives Heliothis development. Best, worst, and intermediate weather years are used to generate a range of predictions for impact of Heliothis on yield. A simple search equation is used to model attack by natural enemies. Decisions are for single fields or small sets of fields and must be updated at least weekly.