This photo clearly shows the correspondence between the plant growth stage and timing of the hail damage and ultimately yield loss. Jeff Mathesius, Pioneer agronomy research manager, provides estimated yield losses based on the timing of the hail and corn growth stage.
V5: When hail occurs at this growth stage, it's early enough in the season that the growing point is still protected below ground, resulting in little, if any yield loss.
V8: When hail damage was simulated at this stage about 75 percent defoliation occurred. Much of the growing season remains at this point and because the growing point was not damaged and many new leaves are still emerging, yield loss was estimated at about 6 percent.
VT: At the VT stage tassels are emerging and if the tassel is destroyed, yield potential can be severely limited. There is also the potential for hail to strike the developing ears at this stage and destroy ovules. At this stage, Pioneer imposed about 90 percent defoliation and also destroyed a number of tassels in the process. Pioneer agronomists estimated there would be about 80 percent loss in yield in this demonstrated scenario.
Estimating Yield Loss from Defoliation
Mathesius notes that hail damage also can potentially cause bruising on stalks at any stage, which can lead to a higher incidence of disease and pest damage as the season progresses and in turn result in additional yield losses.
Use this information as a guide and it should not be the only factor in making decisions.