The easy answer is to say tar spot and disease is the cause but as I've looked back on the growing season I'm beginning to thing the crop was doomed from the beginning.  Planting began the second week of April.  It was dry and warm.  That corn emerged fast.  The stuff planted the next week was planted in warm soil but before it emerged it turned cold.  It sat underground for a long time and emergence was very uneven.  We then went through several extremely wet cycles with a very dry cycles.  I think the extremely hot cycles we had during pollination and then grain fill were just too much.  Ears are stunted and light.  Some genetics have handled it better than other but nothing is good.