The greatest yield reduction in corn due to drought stress generally occurs during the:

The correct answer is the silking/pollination stage because this period is critical for kernel formation, which directly impacts corn yield. During silking, the tassels shed pollen, and the silk emerges from the ear to receive the pollen for fertilization. If drought stress occurs during this time, it can lead to poor pollination, resulting in reduced kernel set and thus, significantly lower yields. The physiological processes that support successful fertilization require adequate moisture, and without it, the potential for a full ear and good grain development diminishes greatly.

In contrast, the other stages can also impact yield, but they do not have as critical an effect on the final kernel number. During the vegetative stage, although drought can stunt growth, it does not directly affect potential kernel set. Ear formation is important, but it is still earlier in the life cycle, and the kernels themselves have not been formed yet. The grain filling stage is crucial for the maturation and development of kernels after pollination has successfully occurred, but by this point, the outcome is largely determined by the conditions faced during pollination. Therefore, the silking/pollination stage stands out as the most susceptible period for yield loss due to drought.