European corn borer, Ostrinia nubilalis (ECB), is known to infest Irish potato, Solanum tuberosum, but only cause economic damage during the first generation in East Coast potato producing areas. However, in Nebraska, second generation ECB infest potato plants during the bulking period and may reduce yield and/or potato quality. Experiments were conducted between 2001 and 2003 examining the physiological and yield effects of second generation ECB injury to potato in Nebraska. Experimental plots were infested with ECB egg masses to simulate ECB infestation by second-generation larvae; controls received no egg masses. Photosynthetic rates, tuber weights, tuber size grades, solids, and fry quality were measured. Potato plants with ECB infestation had significantly reduced photosynthetic rates on ECB-infested stems and on uninfested stems on the same plant. Reductions in yield occurred in 2002 for one variety, FL1879. In 2001, ECB infestation reduced the average mass of large tubers and increased the amount of small tubers in FL1867 and FL1879. This study indicates that second generation ECB infestation at about 30% infested stems results in economic loss for Nebraska, a contrast to east coast growing conditions.