Is it still on the stalk? If it is I'd bet that you have a late summer grasshopper problem. They can terrorize a good crop in a fairly short amount of time. I've included some pics below. To control these I usually apply a little Sevin dust (insecticide) or you can look for organic alternatives at your lawn and garden store or feed store. Just make sure to wash the corn very well before you eat it if you use pesticides or just go ahead and harvest now if you'd rather.
