Thanks to a very wet spring in many areas, lots of corn fields are flooded or ponded and could remain that way for sometime. But according to a Purdue Extension agronomist, there are multiple factors that influence whether a corn crop can survive the stress.
"No one can say for sure the day after the storm whether a ponded area of a corn field will survive, or whether there will be long-term yield consequences until enough time has gone by such that you can assess the actual recovery of damaged plants," says Bob Nielsen, corn specialist. "We can, however, talk about the factors that increase or decrease the risks of severe damage or death to flooded fields."
First, plants completely submerged are at higher risk than those partially submerged because those partially submerged may continue photosynthesis at a limited rate.
The amount of time a plant is ponded directly relates to its risk of death. The longer an area remains ponded, the higher the risk of plant death.
"Most agronomists believe young corn can survive up to about 4 days of outright ponding if temperatures are relatively cool — mid-60s or cooler; fewer days if temperatures are in the mid-70s or warmer," Nielsen notes. "Soil oxygen is depleted within about 48 hours of soil saturation. Without oxygen, the plants cannot perform critical life sustaining functions. Nutrient and water uptake are impaired and root growth is inhibited."
Even if surface water subsides quickly, dense surface crusts still can form as the soil dries and can increase the risk of failed emergence for recently planted crops. Nielsen said farmers should be prepared with a rotary hoe to break up the crust and aid emergence.
Factors like mud and old crop residues on plants as water subsides can lead to greater stress on plants because they reduce photosynthesis.
"Ironically, such situations would benefit from another rainfall event to wash the mud deposits from the leaves," Nielsen says.
Corn plants that have yet to reach growth stage V6 — six fully exposed leaf collars — are more susceptible to ponding damage than older plants. This is partially attributed to young plants being more easily submerged than older, taller plants, and partially because the corn plant's growing point is below ground until about growth stage V6, Nielsen explains.
"The health of the growing point can be assessed initially by splitting stalks and looking at the lower portion of the stem," he says. "Within 3-5 days after water drains from the ponded area, look for the appearance of fresh leaves from the whorls of the plants."