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2020 corn growth and development

Figure. The growing degree days included in each box are specific for the location listed in the box. The number in bold font is the GDDs that have accumulated between May 1 and July 9, 2020, the number after " '19:" is the number of additional GDDs that have accumulated in 2020 than 2019 and the value after "Norm:" is the number of additional GDDs that accumulated in 2020 than the 30-year normal period from 1981 through 2010. Data source: North Dakota Agricultural Weather Network (NDAWN).

2019 corn in NW MN left a bit to be desired.

After a wet spring that led to delayed planting for many in Becker, Clay, Mahnomen and Norman Counties (among a few) and the cooler than normal temperatures that prevailed for parts of the growing season, the 2019 corn crop was unable to accumulate enough growing degree day units to accumulate starch in kernels.  This led in many instances to low test weight corn and discounts at the elevator (see article).  As it did not pay to dry discounted corn, many decided to let mother nature do the drying for them.  The remarkably wet fall led to less than ideal harvest conditions and some people still struggling to take 2019 corn off as late as June 2020.

Needless to say, these series of unfortunate events, along with the forecast record corn planting intentions in 2020 led many to switch from planting corn to some other crop. 

Growing degree days.

Through careful observations regarding corn growth and development, corn agronomists developed a way to use daily high and low temperatures to estimate when important milestones in growth and development will take place.  Each day 50 is subtracted from the average of the sum of the high and low temperatures (temperatures between and including 86 and 50 degrees, respectively) to end up with growing degrees between 0 and 36 degrees.  It is the accumulation of these growing degree days (GDD) over time that can help us to estimate, for example, when black layer (physiological maturity) will occur.

The longer the days to maturity rating for a particular hybrid, the more GDDs needed to reach black layer.  Oftentimes seed companies will provide the GDDs needed to reach black layer for their hybrids.  While 79 day hybrids may require 1890 GDDs, 81, 83 and 85 day hybrids may require 1940, 1990 and 2040 GDDs, respectively.

How is 2020 weather influencing corn growth and development?

Many of those that were lucky enough to get their crops off in 2019 were able to get planted earlier in 2020 than in 2019.  As there was still plenty of corn seeded this year in northwest Minnesota, I decided to take a look at how many growing degree day units have accumulated so far this growing season at many of the locations that host NDAWN weather stations.

Between May 1 and July 9, the 2020 corn crop accumulated between 860 GDDs at Roseau in Roseau County and 1068 at Sabin in Clay County (Figure).  Growing degree day accumulation has been greater than the 30-year normal (1981-2010) at all of the NDAWN locations included in the map, ranging from 38 GDDs greater than normal at Mavie in Pennington County and 141 GDDs greater than normal at Humboldt in Kittson County.  GDD accumulation is also greater in 2020 than in 2019, ranging from 91 greater in Warren in Marshall County to 204 GDD greater in 2020 at Ada.  We can all hope that if the 2020 growing season continues plugging along so that it isn’t a hard frost that ends the growing season, there will be plenty of time for both the crop to reach test weight (56 lb/bu) and fast in-field drying to take place.

What has your 2020 corn crop experienced?

A team of university-based agronomists and climatologists developed an online tool called the Corn Growing Degree Day (GDD) decision support tool.  This tool compares climatological averages, or high and low temperatures for each day at a US location that you select, to the conditions that the crop has experienced during the current growing season.  You can easily change the date that you planted, your days to maturity and GDDs to black layer to better approximate what your crop has experienced and see when the climatological model suggests that your crop will reach maturity.

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