Genetically-modified hybrids with corn rootworm (CRW) protection have been commercially available for six years. Hybrids with the Bt CRW traits are more expensive and initially were available in limited supply. Corn rootworm feeding pressure typically decreases on late planted/replanted corn. Producers were asking if the additional seed costs were justified and, if they could only get a limited supply of the Bt CRW hybrids, when should they be planted for maximum response. Marlin Rice, ISU Extension entomologist, conducted an initial 3-year study (2003–2005) in Central Iowa. The objective of this demonstration was to compare the corn root feeding damage, yield, and economic response of a Bt CRW hybrid with its non-Bt CRW isoline at three planting dates in a continuous corn rotation in Northern Iowa.