Growth stage greatly influences whether ponding or saturated soils kill, severely stunt, or mildly stunt corn plants. Plants younger than V6 can survive only two to four days of flooded or ponded conditions. If temperatures are warm (75°F or higher) plants may not survive 24 hours. In plants older than V6, the growing point may be above the water level and the likelihood for survival improves greatly. To confirm plant survival, check the color of the growing point and look for new leaf growth three to five days after water drains from the field. Healthy growing points will be firm and yellowish-white, not mushy and discolored.
Source: Purdue University Corn & Soybean Field Guide 2008 Edition