The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: Dear Corn Experts: I planted my first vegetable garden in late May of this year and have had a pretty successful crop thus far. My problem is with my corn. This evening I picked off five ears of corn that were approximately two times the normal size of sweet corn in girth. Also the kernels were so big that they actually split open the husks. The kernels were also two to three times the normal size of sweet corn and were greyish-white (see photo). I opened another ear that was not completely ripe and it was fine.
Answer: It sounds like the problem with your sweet corn is smut, caused by a fungus. If the problem is smut, eventually these swollen kernels will turn black from the spores produced by the fungus. Spores are to fungi what seeds are to plants. Corn smut is not harmful to humans. In fact, it is considered a delicacy in Mexico. Corn smut infects plants at points of injury. It is common to have smut in the ear, because insects may feed on the silks, thus creating injury and a point of entry for the fungus.