Thermal time (degree-day) totals help anticipate development of the corn crop. Degree-days are calculated using the modified base 50 F method, with a starting date of 15 May. Use our degree day calculator here.
Typical number of degree-days required to obtain various stages of development for a RM 95-105 hybrid are as shown in the table below (courtesy J. G. Lauer, UWEX Agronomy). Research in Illinois indicates that seeds and young plants exposed to cool soil conditions reach development stages at slightly fewer GDD that usually observed. Thus, GDD work best for predicting crop development when the season is "typical," and become less reliable when the season is not (which is also when you would most like to know!).
|1200||VT - tassel|
|1550||R3 - milk|
|1900||R4 - dough|
|2200||R5 - dent|
|2400-2600||R6 - black layer|
You can correct GDD values from the May 15 starting date map for your planting date by adding additional GDD from Map 2 or Map 3 as appropriate.