Is your corn drowning?
The "derecho" weather phenomenon that's swept through the U.S. the last 2 days has brought even more rainfall to some already-waterlogged areas, leaving some corn fields looking more like fishing holes.
"Recent intense rainfall events (technically referred to as 'toad stranglers' or 'goose drownders') have caused flooding of low-lying corn fields or ponding (standing water) in poorly drained swales within fields. Other areas within fields, while not technically flooded or ponded, may remain saturated for lengthy periods of time," says Purdue University Extension corn specialist and agronomist Bob Nielsen. "What are the prospects for recently submerged corn fields or plants simply enduring days and days of saturated soils? The flippant answer is that such suffering crops will survive until they die."
So, what's it all doing to your crop already in the ground? It depends primarily on 2 things, Nielsen says: Depth of the water and how long the plants are submerged. Both variables affect young plants' ability to continue photosynthesis, and how long that process is limited or interrupted altogether will dictate whether your plants live or die.
"Plants that are completely submerged are at higher risk than those that are partially submerged. Plants that are only partially submerged may continue to photosynthesize, albeit at limited rates," Nielsen says. "The longer an area remains ponded, the higher the risk of plant death. Most agronomists believe that young corn can survive up to about 4 days of outright ponding if temperatures are relatively cool (mid-60's Fahrenheit or cooler); fewer days if temperatures are warm (mid-70s Fahrenheit or warmer)."
Even if plants are peeking out of the water and not totally submerged, damage can come from the ground up; if the soil's completely saturated, oxygen levels are depleted after about 2 days, preventing plants from drawing nutrients and water from the soil and ultimately holding back root development.
How far along your corn crop is also dictates how much damage it will sustain from ponding water, Nielsen says. The older, the better; if your plants are below the V6 growth stage, they're more prone to damage based mostly on the greater likelihood the growing point will be under water. If that's been the case in your fields, proof of permanent damage is easy to find with a simple scouting procedure.
"The health of the growing point can be assessed initially by splitting stalks and visually examining the lower portion of the stem," Nielsen says. "Within 3 to 5 days after water drains from the ponded area, look for the appearance of fresh leaves from the whorls of the plants."
Once ponding water's subsided and you've reached the point at which you can enter your fields to do that kind of scouting, the crop dangers don't end. The combination of crusting soils, corn roots weakened by the high water and soil nutrient movement can make the standing water's impact last beyond the end of soggy conditions.
"Extended periods of saturated soils after the surface water subsides will take their toll on the overall vigor of the crop. Some root death will occur and new root growth will be stunted until the soil dries to acceptable moisture contents. As a result, plants may be subject to greater injury during a subsequently dry summer due to their restricted root systems," Nielsen says. "Nutrients like nitrogen are rapidly remobilized from lower leaves to upper, newer leaves; resulting in a rapid development of orange or yellow lower leaves.
Because root function in saturated soils deteriorates, less photosynthate is utilized by the root system and more accumulates in the upper plant parts. The higher concentration of photosynthate in the stems and leaves often results in dramatic purpling of those above-ground plant parts."