A great deal of field work has been done over in the week. As corn is being planted across the eastern Corn Belt and another growing season has begun, it will be time to walk and scout fields. Once the corn is planted, the next critical event will be uniform emergence. Many producers have read or heard that it takes about 100 to 120 Growing Degree Days (GDDs) for corn to emerge, but what does that mean?
A GDD (also referred to as Growing Degree Units) is a calculation based on daily high and low temperatures. This calculation helps to predict stages of growth in corn based on an accumulation of heat units or GDDs. The basic formula for calculating GDDs is: add the daily maximum temperature to the daily minimum, divide by 2, then subtract 50. The value calculated by this formula is the total number of GDDs accumulated in one day. It is a fairly simple equation with a few limitations: The highest maximum temperature that can be used in the equation is 86 degrees F (even if actual temps are higher) and the lowest value for the low temperature that can be used is 50 degrees F (even if actual temps are lower). The reason for these limits is that corn growth and development is significantly reduced and/or stopped at temperatures above 86 degrees F and below 50 degrees F.
When daily accumulations of GDDs (accumulated after planting) add up to a total of 100 to 120GDDs, corn seedlings should be emerging. While watching fields for corn to emerge this spring, keep in mind that daily temperature fluctuations will play a significant role in determining the period of time between planting and emergence.