For areas with only moderate rainfall, Nafziger says wait and see what happens. He says there may be enough nitrogen to carry the corn, but if the weather reverts to more rain, with warm temperatures, then supplemental nitrogen may be needed.
If you have not had the opportunity to apply nitrogen, Nafziger says do that as soon as possible with normal or even lower N rates.
While there was an initial chance that 2013 corn could use some of the leftover nitrogen from the 2012 crop, it has likely been lost into the environment, and along with some of the nitrogen you may have applied last fall or this spring. The unfriendly planting weather has also become unfriendly for retaining nitrogen in the soil, and in a form that is available to your corn. The decision of whether to apply more nitrogen depends on many factors, but primarily how much rain has fallen that might wash the nitrogen out of your field.
Source: FarmGate blog