Producers continue to plant corn earlier every year, if possible. Due to wet weather in 2007, producers were not able to plant as early as desired. Fifty percent of the statewide crop was planted by approximately May 6, in contrast to April 25 in 2006. Producers tend to plant earlier for several reasons: larger acreage per producer, less spring tillage, advancements in hybrid tolerance to cold, and seed treatments. Planting the crop during the optimum window is important to achieving high yields. This research is conducted to identify that window.