The disheartening picture of corn under water is from the Crop Watch '14 field after 3 inches of rain over three days. The good news is that only about a quarter to perhaps half an acre of the entire field is affected by ponding.
That's not the case in some other areas. Reports from southern counties say some farmers have already replanted spots once, and many of those spots are wet again. A considerable amount of planting remains to be done. Reports of spotting in low spots or replanting whole fields have filtered in form across the region. Water is the main culprit – cool weather didn't likely help.
Crop Watch 6/2: What a Difference Nine Days Makes to Young Corn
How much flooding affects yield depends upon the amount of time the area is flooded, and how cool or warm the temperature is while the corn is flooded. Obviously some of the corn in this picture will be hard-pressed to recover. However, most of it is right at the five-leaf stage, with the growing point below the ground. There is the possibility for regrowth, although that often doesn't happen in these ponded areas.
Part of the problem now is that once these areas dry up, and you determine little or no corn will make it, is there time and is it economically worth it to replant?
The Purdue University Corn & Soybean pocket Field Guide and its companion iPad app, indicate that based on averages, if you replant today and achieve 32,000 plants per acre, the original seeding rate in this field, you can expect about two-thirds of normal yield. Also factor in that the corn will likely be wetter at harvest when you combine those spots with the rest of the field.
Crop Watch 6/6: Time to Watch for Problem Spots to Appear
Compare that to this example: If you planted May 5 and still have 18,000 plants per acre, you could still expect about 87% of original yield. The numbers don't appear to favor replanting drowned-out spots this late in the season.