In 1996, Arizona cotton growers began using insect growth regulators (IGRs) to control silverleaf whitefly. This study uses GIS data recording pesticide use at the section level for the entire state to address two questions. First, what factors explain the intensity of IGR adoption? Second, how has IGR adoption affected overall insecticide use? A two-stage model is estimated that accounts for both the endogeneity and censoring of the adoption intensity variable. Results suggest conventional insecticide use fell by 3.66 applications for every IGR application. Statewide, net insecticide costs savings in 1996 alone were $9.5 million, over $28,000 per adopting operator.