Infestation of sweet corn (Zea mays) at harvest by european corn borer (Ostrinia nubilalis) was examined in 16 hybrid/harvest date combinations from 1994 through 1996 in central Pennsylvania. Two general periods of sweet corn ear infestation levels were observed. Infestations, expressed as proportion of ears infested, were 0.11 (11%) or lower in 10 of 11 plots harvested from 21 July to 23 Aug., whereas they were noticeably higher (30%–88%) in September and early October. Infestations expressed as larvae per ear showed the same temporal pattern. A nonlinear (sigmoidal) relationship was found between degree-days from 1 Jan. and proportion of ears infested. The higher infestations were caused by the second-generation larvae of the bivoltine ecotype. Based on these relationships, a risk-prediction system is proposed that anticipates, at planting, harvest infestation by using predicted harvest dates of sweet corn, european corn borer life stages, and infestation levels. Examples are presented for multiple plantings and hybrids for a specific site and a landscape (Pennsylvania). The risk prediction system we propose will allow growers to anticipate the risk of ear infestations at planting time, thus providing predictions that would help with management decisions.