Farmers are starting to plant corn in southern Georgia and other areas of the Southeast. Rome Ethredge, in the Seminole Crop E News blog (link), pointed out that corn needs about 100 GDD to emerge from seed to seedling, and that areas in his county are reaching that now. In fact, in spite of the cold winter, corn GDDs are ahead of the last two years and comparable to 2012 for the same time frame.
If you want to calculate corn growing degree days for your area, you can use these sites:
For Georgia, http://www.georgiaweather.net. Calculate corn degree days using a base temperature of 50 F and a cutoff temperature of 86 F.
For other areas, use AgroClimate http://agroclimate.org/tools/Growing-Degree-Days/ and use the drop-down menus on the left to choose the appropriate parameters. Note that AgroClimate allows you to choose from four different base temperatures.