Growing Degree Days (GDD) and Rainfall Through July 17th

Jarrod O. Miller, Extension Agronomist,

All of our variety trials are almost finished with pollination, including some we observed in Western Maryland. Many nights have been in the upper 60s, which is good for growth, with only a few days in the low 90s. Therefore, temperatures should not be a significant negative factor in growth, unlike the lack of rain we have observed. Anything planted in late May is probably undergoing pollination, should see ideal temperatures for pollination in those fields.

V12: 870 GDD – Ear size, kernel number are being determined
VT: 1135 GDD – Pollination can begin
R1: 1400 GDD – Silking, pollination
R6: 2700 – Blacklayer

Table 1: Growing degree days accumulated through July 17th from the beginning of each week.

  Sussex Kent New Castle
22-Apr 1790 1750 1690
29-Apr 1738 1704 1657
6-May 1630 1594 1559
13-May 1526 1488 1461
20-May 1414 1382 1368
27-May 1256 1223 1219
3-Jun 1104 1071 1069
10-Jun 981 954 955
17-Jun 845 827 826


Mid-week rainfall certainly helped, but as you can see from this DEOS image below, variability ranged from a few tenths to an inch across the state. We believe there is an error at the Georgetown station where no rainfall recorded. While Georgetown still has a total accumulation of 20 inches since late April, it’s not sitting on the surface anymore. Many cornfields are starting to look like fields of agave, so if you have irrigation use it! We may get relief in some rainfall next week, but until then it is critical to have good soil moisture during pollination.

24 Hour rain fall captured on July 18th, 9 am.

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