Source: University of Illinois

A couple of different corn ear rots have been reported in Illinois. Diplodia ear rot, caused by the fungus Stenocarpella maydis (formerly Diplodia maydis), has been reported at moderate to high levels in areas of the state that received excessive rain throughout the growing season. Aspergillus ear rot, caused by the fungus Aspergillus flavus, has been reported in areas that have been extremely hot and dry.

Symptoms of Diplodia ear rot.
Ears affected by Diplodia may have a white mold growing on and/or between the rows of corn. Ears affected within two weeks after silking may be completely "mummified," while in later infections, a light, cottony growth may be observed growing on the ear. Speck-sized fruiting bodies (pycnidia) will be formed by the Diplodia ear rot fungus, and often can be observed on the sides of the kernels. 

More information