It can be very difficult to predict survivability of damaged plants by simply looking at the damage itself, says Bob Nielsen, Purdue University corn specialist.
"Young corn has an amazing capacity to recover from early season damage, but farmers need to exercise patience to allow damaged plants to visibly demonstrate whether or not they will recover, he says. "Damaged, but viable plants will usually show noticeable recovery within three to five days with favorable weather and soil moisture conditions."
Yield losses in corn result from plant death and leaf area reduction. However, when the damage occurs early in the season, Nielsen says yield loss is not directly proportional to a reduction in the number of plants per acre.
"The surviving plants surrounding an absent plant can compensate by increasing their potential ear size or by developing a second ear," he says.
To estimate severity of defoliation, growers must first determine leaf stage. Younger leaf stages can more easily rebound from hail damage.
"Leaf damage by hail usually looks worse than it really is," Nielsen says. "Tattered leaves that remain green and connected to the plant will continue photosynthesizing."
Final yield losses depend on a number of factors, including planting date, leaf stage and plant population per acre.
After several days, growers also can check for whorl and stem bruising. While this typically does not result in stalk lodging or stalk rot development, the plant may be deformed or be more susceptible to bacteria.
More information about hail damage and tables with expected yield loss data are available at http://www.agry.purdue.edu/ext/corn/news/timeless/HailDamageYoungCorn.html