This paper studies the effects of enforcement on illegal behavior in the context of coca cultivation in Colombia. We explore the deterrent effects of a large aerial spraying program designed to curb cocaine supply. We exploit variation induced by a diplomatic friction between the governments of Colombia and Ecuador over the possible negative effects of spraying campaigns over Ecuadorian territory. As a result of this friction, Colombia pledged to stop spraying campaigns within a 10 km band along the border with Ecuador in 2006. We estimate the effects of spraying on cultivation by regression discontinuity around the 10 km threshold and conditional differences in differences, using satellite data for 1-square-km cells. Our results suggest that spraying one additional hectare reduces coca cultivation by about 0.02 to 0.065 hectares, consistent with the view that enforcement reduces illegal behavior. However, these effects are too small to make aerial spraying a cost-effective anti-narcotic strategy.