UW Extension Ag Weather

Contour map

Corn Development

May 15 to Present

Corn Development Degree-Day Map

Black and White Image

Earlier Degree Day Maps (available mid-May)

Corn Degree Day Calculator

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.

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!).

GDD STAGE
600 V8
900 V13
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 (Map 1) for your planting date by adding additional GDD from Map 2 or Map 3 as appropriate.