Around here, they graze the corn plants themselves when they are young and tender. The rows along the edge of the woods and where the trails enter the fields often have the leaves all knawed off to the stalk. When the corn gets high enough to provide cover, the deer will actually move into the corn fields and bed down, less bugs, good cover, lots of food. When the ears start forming they'll knaw the ends off them. And when the corn gets ripe of course they'll eat that. During gun season, if the corn is still up, it's typical to drive the corn fields.