Hot & dry: Stress on the corn crop escalates
Prior to harvest
Assuming that pollination occurs successfully, then pre-harvest grain yield estimation revolves around kernel abortion and grain filling. Unfortunately, one cannot begin to estimate grain yield for an individual drought-stressed field until the crop is beyond the milk stage of the grain filling period where the risk of kernel abortion tapers off. The risk of kernel abortion is greatest immediately following successful pollination and decreases to nearly zero by about mid-milk stage of grain fill. Once the crop reaches or surpasses the dough stage of grain fill, the "ballpark" grain yield potential can be estimated by documenting effective plant populations and sampling ears throughout the field.
Pray for rain or turn on the irrigation.