Increased GDUs Hurried Crop through Grain Fill Period

Guest blog by
John Toft, CCA

We’ve all heard the expression, “Haste makes waste.”  When we hurry through a job, the job is not done as well or as thoroughly as it could have been.  The same is true for corn production.  The increased growing degree units hurried this year’s crop through the fill period, thus reducing yield in most instances.

The following statistics provide a seasonal comparison originating from the temperatures and growing degree units over the past 34 years at my farm near Tekamah, Neb.  You’ll see comparisons between the 2011 season and last year, plus two other particularly challenging years.  Pay close attention to the nighttime lows greater than or equal to 700F, the high greater than or equal to 900F, and the days with a low greater than or equal to 700F and a high greater than or equal to 900F.  

As noted in an earlier post, when night-time temperatures do not fall below 70 degrees, plants don’t get time to rest.  When the plants don’t rest, they continue to work excreting sugars through open stoma rather than utilizing those sugars for grain fill.  The plants run out of energy causing tip back on ears and reduced yield.


This graph shows GDUs from April 1 to August 11 as well as Stress Units observed during this same time period. You'll notice that GDUs were adequate, but the amount of Stress Units were well over the 33-year average.

Note: click on the graphs to enlarge,
then click the “back” button to return to this post.

This graph shows comparisons for the month of July, a critical month for pollination and beginning grain fill stages. Pay particular attention to the days with possible stress units as well as the days with lows greater or equal to 70.

Does the late planting combined with limited rainfall and extreme heat mean that this fall’s harvest will be bad?  No, most farmers will still get a good crop.  It’s just that this year’s crop will most likely not reach its full yield potential.  For example, a 20% yield loss on a field that had a 220-bushel per acre potential will still see yields of 175 to 180 bu/A.