ABSTRACT RUNOFF losses of fonofos (insecticide), alachlor, atrazine, and cyanazine (herbicides) with sediment and water were measured under natural rainfall con-ditions for six small watersheds planted to continuous corn with conventional, till-plant, and ridge-plant tillage systems. Losses were very dependent on the time between pesticide application and the first runoff event. Soil sampling indicated that pesticide half-lives were about 2 wk (except for atrazine, 1 to 2 months), with pesticides remaining concentrated in the top 5 cm. Not quite 50 percent of the average fonofos loss was with water, whereas from 80 to 90 percent of the average herbicide losses were with water. Decreased runoff and erosion for the till-plant and ridge-plant tillage systems relative to conventional resulted in decreased pesticide losses, but pesticide concentrations in sediment and (or) water were sometimes higher for conservation tillage systems.