Kernel fill time

The biology of the corn plant after the initial ten days of movement of glucose to the developing kernels is consistent with nearly all hybrids.  This Corn Journal blog of August 2016 applies even in the USA Midwest wild summer of 2019.

​As the corn embryo develops, and the cytokinins accumulate in the pollinated ovule after the first 10 days, there is a constant translocation of sugars to each kernel for each day.  The total daily movement continues for about the next 40 days, almost regardless of daily variable rates of photosynthesis due to cloudy weather or leaf damage from disease.  Sugars are drawn from all leaves and even those stored in the stalk pith tissue.  The total draw to the ear is determined by genetics of the variety, environmental factors including minerals and the number of kernels.  The number of kernels is also determined by genetics and environment factors such as minerals and especially water available during ovule formation and pollination. 
 
The daily transfer of sugars during days 50 to 60 of grain fill is greatly reduced until the abscisic acid affect causes thick cell walls to form at the base of the kernel, cutting off the sugars transfer into the kernel and the movement of water from the kernel.  This is known as the black layer.
 
Sugars translocated to the ear are sugars not available to other living tissue in the plant.  Roots are especially dependent on the same sugars to support metabolism functions, including warding off the potential microbe invaders.  Starving roots, as they rot, eventually reduce water uptake and, if insufficient water to meet the transpiration rates from leaves, a permanent wilt will occur.  With the wilt, movement of sugars to the kernels is stopped, abscisic acid takes over, causing the black layer to form a base of kernel.  The consequence is light grain weight on the affected ear.