In a planting date study conducted at Arlington, the first planting date of April 15 was beginning to emerge on May 7. For corn to emerge from the soil, it typically requires about 125 GDUs where GDUs = ([Max. air temperature + Min. air temperature]/2) – 50. The accumulated GDUs to emergence varies by 15 to 60 GDUs due to a number of factors like soil texture (fine: add 30-60 GDUs; coarse: subtract (30-60 GDUs), seeding depth (add 15 GDUs for each inch below 2 inches), seed zone moisture (below optimum add 30 GDUs), amount of residue on the surface (more than 75% residue add 30-60 GDUs), and hybrid differences for development.

On May 7, the coleoptile of about 50% of the corn plants was visible at the soil surface. This particular field at Arlington required 22 days to emerge and as you can see in Figure 1, emergence was right on schedule according to GDU accumulation. Often in Wisconsin, I have seen corn take 28 to 35 days to emerge due to the cool soil temperatures. In general, I do not get too concerned with slow emergence until about 28 to 30 days have passed since planting. Most of the seed treatments used today in corn production offer 45 to 60 days protection from many of the insects and diseases that attack corn seedlings.