Our first corn planting date this year was April 10. It was the earliest we have ever planted corn at Arlington. We might have been able to plant a couple of days earlier, but there was still frost under the corn residue piles when we started working the field, so we decided to let the soil warm up a little. The previous early planting date was April 13 in 2004, April 14 in 2006 and April 15 in 2002, 2003, and 2005. We have planted corn when there was still snow in the fence lines (2007) and when up to 4 inches of snow fell on the plots after planting and prior to emergence (multiple years).

When cool, wet weather occurs (which will likely happen in April in Wisconsin - sometimes even May and June!), growers are often concerned about early planting dates and the impact these weather systems can have on grain yield. Since 1991 we have annually conducted a planting date trial at Arlington using multiple hybrids. Figure 1 shows grain yield of full-season hybrids (average = 107 d RM) over the last 10 years.

The planting date producing maximum grain yield is May 1. Most of the time (>80%) the planting date producing maximum grain yield occurred in either April or early May, but there are a few years (2002 and 2003) when planting dates in early May did not produce greatest yield.

One possible reason for the yield decrease is the onset of cool, wet weather within 48 hours of planting, Under these weather conditions we have lost trials to stand emergence (2006 in Seymour and Fond du Lac). In these planting date trials in 2002 and 2003, we did not lose stand, but wonder whether other non-lethal effects on plant growth and development occurred such as seedling diseases. Unfortunately not much hard data and only conjecture and observations. We may have inadvertently repeated the situation this year when we planted ~500 plots on April 17 into chisel-plowed and no-till fields and cool, wet weather moved in immediately and stayed for a few days - stay tuned!

The planting "window" or period of time when grain yield is within 95% of the maximum yield date is about 21 to 28 days at Arlington. By May 15 we are clearly at the point where grain yield is decreasing. Grower face a larger yield reduction planting too late rather than too early. After May 15 grain yield decreases at the rate of 0.5 bu/A per day and accelerates to 2.5 bu/A per day on June 1 (Figure 1). Not only is grain yield decreasing, but grain moisture increases causing greater drying costs in the fall.

Numerous factors allow us to plant corn earlier than ever including cold-stress tolerant hybrids, improved seed treatments, and better planting equipment. As farmers manage more acres, they may or may not need to start earlier depending upon the width of their equipment and how many days is required to plant. Insurance requirements need to be considered since some policies will not cover extremely early (and late) planting dates.

In Wisconsin, we have also been caught when a late frost occurs. In 1992, corn planted early was past the V5 stage of development when the growing point moves above-ground and a late frost on June 20 killed large acreages of corn. This is likely a rare event, and I would still look to plant early if field conditions are acceptable.

Figure 1. Response of full-season corn hybrids to planting date between 1999 and 2008 at Arlington, WI.