Growing degree days (GDD), also known as heat units, are calculated by taking the average of the high and low temperature in a day, minus the base temperature of 50°F. The optimal number of growing degree days varies depending on the crop and maturity. Tracking growing degree days is helpful in monitoring your crop progress throughout the growing season. Cumulative Iowa average growing degree days (GDD) are ahead of last year at this time. Des Moines is at nearly 2900 cumulative GDD since the beginning of March, however Charles City and Cherokee are at about 2300 GDD.

The second graph shows a comparison of GDD for a few years between 2012 and 2018 at various locations. As you can see, the 2018 Iowa average GDD totals were behind the other years early on until about mid-May, but with the hot weather lately have surpassed the GDD’s accumulated at this point in other recent years such as 2017, 2016, and 2014.

According to the most recent USDA Crop Progress report, 42% of Iowa’s corn crop has dented, which is significantly ahead of the 5- year average of 21% dented. Missouri and Illinois have 79% and 63% of their corn crop dented, respectively.

Michelle Mensing, Research Analyst, Decision Innovation Solutions (DIS). DIS is an Iowa-based economic research firm which provides regular farm economic research for Iowa Farm Bureau staff & members.