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  what I can tell looking at temperature reports around Indiana today and looking 
  at some fields of emerged corn, I don't believe Sunday morning's low temperatures 
  around the state were lethal for corn that was planted and/or emerged. Cloud 
  cover helped us avoid frost also, so we dodged that "bullet" also. Emerged corn 
  at the Purdue Agronomy Farm showed no evidence of injury this morning. Some 
  fields in far northern and/or eastern Indiana may have experienced some snow 
  cover Sat night and Sunday, but that will not necessarily be lethal to an emerged 
  corn crop either. 
Isolated frost forecast for Monday morning (Apr 25) may damage aboveground leaves of emerged plants. The forecasted temperatures in the low to mid 30’s, however, should again NOT be lethal to growing points.
Bottom line is that I doubt that replanting will be necessary for much, if any, of the early planted corn in Indiana. Growers concerned about such a decision should exercise patience and give damaged fields three to five days to show evidence of recovery from frost/freeze damage.
Growers should be aware that emerged corn over the next few days will likely take on the typical "crappy" yellow-green appearance associated with exposure to such cold snaps. A return to warm sunny weather will help alleviate this ugly state. Of more concern is a bit of fear mongering about the possibility that some planted fields not yet emerged may experience some degree of twisted or corkscrewed mesocotyls leading to belowground leaf emergence and stand loss. This phenomenon is anecdotally attributed to unusually cold soils prior to emergence.
Stay tuned for more information......