Pollination timing in late planted corn

​Time from germination to production of pollen in temperate zone corn is determined by amount of heat per day after germination.  The shoot apical meristem produces leaf and stem cells until it gains the hormonal signals to switch to producing the tassel cells.  This occurs while the growing point is surrounded by the growing leaves usually at about the V6 stage.  The 2019 rain during April and May delayed planting much beyond normal.  Pollination in most fields in Northern Illinois is at least two weeks later than normal.
 
It will be interesting to see if warmer temperatures after planting this season will cause earlier initiation of the shoot apical meristem to tassel cells and consequently fewer leaves.  We attempt to characterize hybrid maturities by daily heat units, with heat units to flowering and/or heat units to abscission layer formation in kernels but actually it is mostly determined by heat for apical meristem differentiation.  Time from pollination to completion of grain fill as the abscission layer cuts off translocation of carbohydrates to the grain is mostly a time factor of about 55 days.  Consequently, the heat from planting to shoot apical meristem differentiation is the most critical factor on determining when these late planted corn fields will have completed grain fill.
 
The 2019 corn season in much of the northern USA corn belt will be remembered as distinct from previous season.