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Date: 8/11/2014

Title: Growing Degree Days in the Corn Belt

Plant growth, whether it is alfalfa or corn needs heat, water and sun to grow. One very reliable way to track how far along or how far behind a crop is developing is to use something called “growing degree days”. Growing degrees days are a measure of heat accumulation used by anyone trying to raise a crop, whether it is hay, corn or sugar beets. The amount of growing degree days helps to predict plant and development rates and whether or not a crop needs more heat or less for a successful crop.

If growing degree day accumulations are above average that would indicate a warm summer, above normal temperatures. Conversely, below normal growing degree day accumulations would indicate the opposite (a cooler than normal growing season).

At this point in the growing season it is important to take a look at growing degree accumulation as the summer growing season is winding down and we start looking at the prospects for the frost/freeze of the year. If crops are behind in development because of a cool growing season, an early frost/freeze could have a big impact on commodities, prices, etc.
As we all remember the winter and spring of 2013/2014 was a cold one and the summer season has had more cold fronts than heat waves. How has that impacted growing degree day accumulations?

The graphic below from the Midwestern Regional Climate Center shows growing degree accumulations from May 1 through August 7.


If we then compared the accumulations in the above graphic to normal values the result is below.


Any color that is light orange to yellow into the green and blue represents areas where growing degree day accumulations have been below normal. Not surprisingly, with the very cool water temperatures in the Great Lakes, we find the biggest growing degree day deficits in the Great Lakes.  

Another area of much below normal growing degree day accumulations is in the western Corn Belt of Iowa, Minnesota and the Dakotas. 

In the eastern and southern areas of the Corn Belt, growing degree day accumulations are trending at or above normal. However, most of the Midwest and Corn Belt is experiencing below normal growing degree day accumulations.

With no indication of a prolonged spell of heat for the remainder of August we will be keeping a very close eye on Canada and points north for a strong, season ending cold front!