Recent heavy rainfall has resulted in a few areas experiencing flooding or ponding within fields.  Though all crops may be affected, this article focuses on flooding effects on corn.  The following comments should be regarded as generalizations.  There are many variables that affect how long corn can tolerate flood conditions.

When soil is flooded or saturated, there is a limited amount of time before free oxygen is consumed in the soil.  When there is little or no oxygen left, corn and other crops do not grow well.  Under these conditions, corn roots cannot take up water or nutrients.  If water is standing over the leaf tissue, injury to this tissue occurs rapidly.  If the corn growing point is submerged or below the soil surface in saturated soils, this growing point may be killed within a few days.

Crop injury from flooding or saturated soils occurs more quickly as temperatures rise.  This is simply related to the level of biological activity and resulting depletion of oxygen.  Damage from flooding or soil saturation tends to occur more slowly under cool conditions.  The exception is that, at around 45°F, corn is not growing very fast but pathogens, like Pythium, are still active.  Consequently, cool weather is not always positive when field conditions are wet.  It is also generally true that tender leaf tissue is more quickly injured than either older tissue or seed that has not yet germinated.  A very young corn plant can easily be injured by ponding or flooding, whereas an older plant with toughened leaf and stem tissue might last longer under the same conditions.

A number of experts will tell us that corn seed is pretty tolerant of flooding or soil saturation as long as the seed coat stays intact.  Once the radical or shoot penetrate the seed coat, the developing seedling cannot tolerate more than a few days of excess water.  For the emerged corn plant, growth will stop within a couple days following soil saturation or flooding.  As soils go anaerobic, the corn seedling will begin to decline rapidly.  Under flooded conditions, the corn seedling will be irreversibly damaged within 2 to 3 days.

Several factors influence the rate and extent of damage from flooding or soil saturation.  Temperature is one factor that has already been mentioned.  Corn will tolerate flooding a lot longer under cool, than under warm conditions.  Water depth is another factor.  Although saturated soils are inhospitable for root growth, corn seedlings can tolerate these conditions longer when the leaf tissue is exposed to the air.  If the leaf tissue is under water, plant death can occur in less than 48 hours.  The only way to accurately assess the situation is to revisit the field(s) often, digging and splitting sample plants to observe plant health.

When determining how to manage fields that have been flooded, the hardest decision will relate to the till or no-till question.  Once saturated soils lose oxygen, they can be slow to regain normal aeration.  Tillage can help, but may not be allowed or even practical.  Rushing back to replant a saturated field could result in soil compaction or poor stand establishment.  Weed control is often compromised by the flooding or soil saturation, so available emergency weed control options should be considered.

If the decision is made to replant only ponded or worst parts of fields, be aware that these very late planted areas could become highly prone to insect and plant disease problems.  It may be necessary to create an access path into these areas so that timely weed, insect, or disease control can take place.  Also, these late planted patches may complicate timing of fungicide or post-emergence herbicide applications because of differences in crop maturity.