Planting dates are earlier today than ever before, with 50 percent of the crop planted by April 25 last season. In general, research has shown a small yield loss with very early planting dates and a larger yield loss with later planting dates. Research conducted during 1998-2000 showed that planting approximately between April 20 and May 20 resulted in 100 percent yield (see Iowa State University Extension's Planting Guide). Based on newer research (2003-2006), we believe that this window is actually earlier; corn can be planted prior to April 20 and reach 100 percent yield.