Heavy rains in mid- to late May have saturated some corn fields or even flooded fields. Periods of early-season flooding or soil saturation can sometimes cause immediate problems for small corn plants, said Kraig Roozeboom, Kansas State Universoty Research and Extension crop production specialist.

If small corn plants are affected by these conditions, it can have season-long implications, he warns.

“Saturated soils inhibit root growth, leaf area expansion, and photosynthesis because of the lack of oxygen and cooler soil temperatures. Yellow leaves indicate a slowing of photosynthesis and plant growth. Leaves and sheaths may turn purple from accumulation of sugars if photosynthesis continues but growth is slowed,” he said.

Corn plants can recover with minimal impact on yield if the plants stay alive and conditions return to normal fairly quickly, Roozeboom added. Saturated soils early in the season can have season-long effects on root growth, however.

“A saturated profile early in the season can confine the root system to the top several inches of soil, setting up problems later in the season if the root system remains shallow. Corn plants in this situation tend to be prone to late-season root rot if wetness continues throughout the summer, and stalk rots if the plants undergo mid- to late-season drought stress. Plants with shallow root systems also become more susceptible to standability problems during periods of high winds,” Roozeboom said.

What if the corn were actually under water for several days? Young corn plants typically can tolerate full submersion for up to 48 hours with minimal impact on yield, he said. If the conditions last longer than that, the outlook changes a bit.

“If flooding occurs before the V6 stage of growth, when the growing point is at or below the soil surface, flooding that lasts more than two to four days can impact season-long plant growth and grain yield, or cause significant plant mortality. The chances of plant survival increase dramatically if the growing point was not completely submerged or if it was submerged for less than 48 hours,” Roozeboom explained.

Temperatures at the time the soil was flooded or saturated can influence the extent of damage, he added. Cool, cloudy weather limits damage from flooding because growth is slowed and because cool water contains more oxygen than warm water, he said. Warm temperatures, on the other hand, can increase the chances of long-term damage.

Flooding can increase the incidence of moisture-loving diseases like crazy top downy mildew, said Doug Jardine, Kansas State Research and Extension plant pathologist. “Saturation for 24 to 48 hours allows the crazy top fungus spores found in the soil to germinate and infect flooded plants.”

The fungus grows systemically in the plant, but visual symptoms will not appear for some time, he said. Symptoms include excessive tillering, rolling and twisting of upper leaves, and proliferation of the tassel. Eventually the tassel can resemble a disorganized mass of small leaves, hence the name “crazy top.”

Source: Kansas State University