After the Flood

Saturated Cornfields Face a Host of Late-Season Risks

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Crazy top is a late-season corn disease favored by flooded field conditions early in the season. Growers should be on alert for it this summer. (Photo courtesy Tamra Jackson-Ziems)

ROCKVILLE, Md. (DTN) -- So your corn crops survived a tough spring -- flooding, saturated soils and cool temperatures.

Don't relax just yet.

Your crop may be at risk for a host of diseases, nutrient deficiencies and standability issues later in the summer.

"Plants that had wet feet for a long time early on are smaller, weaker and more vulnerable to any stress that occurs later in the season," explained Purdue University corn agronomist Bob Nielsen. "It's not a good way to finish strong."

Keep an eye on those fields for the following complications:

1. ROOT AND STALK ROTS

Cold, wet soils and slow emergence put corn seedlings at high risk for infection by fungi like Pythium and Fusarium, said University of Nebraska plant pathologist Tamra Jackson-Ziems.

Just because a corn plant survived those conditions doesn't mean it's home free.

Those infections can remain in the plant and surface as late-season diseases or simply leave a plant weakened and more vulnerable to stalk rot fungi later, Jackson-Ziems explained.

Stalk rots hollow out the stalk, and plants suffer from yield loss and lodging. See a UNL scouting guide for common stalk rots and their symptoms here: http://bit.ly/….

Root rots may also be lingering in a flood-survivor, Jackson-Ziems said. Fields infected with Pythium or Fusarium root rot will be stunted, discolored, grow unevenly and yield poorly. See an Iowa State guide to them here: http://bit.ly/….

A condition called "weather crown stress" can also result when cold, saturated soils deprive young crown roots of oxygen, according to Kansas State University agronomists. This condition, which affects southern hybrids in particular, can also put you at higher risk for stalk rots. Read the Kansas State article here: http://bit.ly/….

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2. CRAZY TOP AND BACTERIAL ROTS

Crazy Top is an easy disease to spot, as its name implies. Corn tassels and upper leaves grow wildly and roll and twist into giant Medusa-like structures. Corn ears can also get caught up in the mess.

The downy mildew fungus that causes Crazy Top thrives in flooded fields, Jackson-Ziems said.

"The disease has swimming spores, so it has to have those saturated soils to infect," she explained. "It will infect early on, but you don't see the symptoms until later when the plant puts on tassels and an ear."

Bacterial infections can also rot a plant later in the season, most commonly within the stalk. Silt or soil sitting on top of previously flooded plants can help introduce these pathogens that enter through the whorl or plant wounds.

"It causes the whole plant to die and it stinks really badly," Jackson-Ziems said. "Often you'll smell it before you see it."

3. RESTRICTED ROOTS AND SMALLER PLANTS

Corn roots that were flooded early can become restricted for a variety of reasons, from heavily compacted soils to root rots and stunted growth in saturated, oxygen-starved soils.

Nielsen says compaction will be a major cause of this problem in Indiana this year.

"Once the rain started in late April, I don't think there were many days when the soil was fit for any tillage or fieldwork," he said.

Plants with restricted root systems will be at a greater risk for lodging later in the season. They're also likely to be poor performers throughout the season.

"If it turns dry, they'll be the first to suffer, and if we keep getting too much rain, they'll be the first to suffer," Nielsen said. "They're just not able to avoid effects of severe weather easily."

Without a good root system, the plants will be smaller and will struggle to produce ears and fill them, he added. Kernel abortion can occur and reduce yield quickly.

Even if ears do fill well, the smaller plant may have to cannibalize itself during grainfill, leading to hollowed stalks prone to lodging.

4. NUTRIENT DEFICIENCIES

"With rains throughout May, there are a lot of opportunities for loss of soil nitrate by leaching in coarser, sandier soils or denitrification (nitrogen lost via gases) in heavier soils," Nielsen said.

The same holds true for sulfur, which is also prone to leaching from soils in sulfate form, he added.

Sometimes nitrogen and sulfur just move lower in the soil profile and are available to deeper roots later in the season. In other cases, they completely leave the soil profile and a true deficiency results.

Sulfur-deficient plants will look yellow, with striping of the leaves.

Nitrogen-deficient plants will appear yellow and stunted. Yellowed or dying (firing) leaves lower in the canopy are a good sign of nitrogen loss, Nielsen said. This occurs when plants remobilize nitrogen from the lower stalk and leaves up to newer leaves.

"It's a crude indicator but an indicator nonetheless," Nielsen said. If you spy this phenomenon close to tasseling time, it may be worthwhile to consider a rescue nitrogen application with a high clearance rig, he added.

For more help on testing for nitrogen loss, see this Iowa State guide: http://bit.ly/….

For more details on all the late-season effects of ponding or saturated corn fields, see an article from Nielsen here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/AG)

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Emily Unglesbee