Wet Spring Questions

Assess Your Stand: Is it Disease, Flood, Cold or Herbicide Injury?

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Scouting stands will be essential after widespread flooding and cold in the Midwest this spring. (DTN photo by Scott R Kemper)

ROCKVILLE, Md. (DTN) -- Farmers are facing a new version of Paul Simon's famous ditty -- let's call it "Fifty Ways to Lose Your Seedling."

Since late April, young corn and soybean plants have faced cold, wet soils, extensive flooding, soil diseases and herbicide injury.

Walking fields and taking multiple stand counts is essential, but digging up and diagnosing dying or missing plants is equally important to making replant decisions, crop experts told DTN.

Here's a brief overview of the many contenders for crop damage this spring:

DEAD OR DAMAGED SEEDS

Down in southwestern Indiana, the Cooprider family was wrapping up corn planting in late April. They planted one river bottom field with corn on April 25, three days before Mother Nature began an 8-inch deluge of cold rain.

"It's been underwater since April 28," Mike Cooprider said of the ill-fated cornfield. The waters are slowly receding, but almost no corn has sprouted in that field.

Of all the crop damage out there, scenarios like this one alarm Burrus Seed agronomist Stephanie Porter the most.

"My biggest concern right now are fields planted right before the big rain," she said. "Those first 24 hours to 48 hours are critical for the seed." Corn and soybean seeds that take in cold rainwater below 50 degrees in the first two days are at risk for cell damage and even death. (See a DTN article on this phenomenon, called imbibitional chilling, here: http://bit.ly/…).

Dig up seeds and see if they are swollen and soft -- which indicates damage -- or firm and sprouting -- which indicates good health, Porter said.

For now, Cooprider's river-bottom corn seeds are still firm, but no sprouting in sight. His son, Tyler, estimates that nearly a third of their planted acres are candidates for replant this year.

FLOOD-DAMAGED PLANTS

Many early-planted cornfields emerged before heavy rains in late April and early May flooded fields. They face a range of possibilities, depending on how fully submerged they were, how long they were submerged and their growth stage, Porter said.

In cool weather, corn plants can survive up to four days underwater and soybeans can stomach at least 48 hours, said University of Missouri plant scientist Greg Luce, in a university news release on the flooding.

Larger plants require more oxygen, but smaller plants are more likely to be fully submerged, Luce said.

Surviving corn plants should show new growth within three to five days of drying out, he said. However, saturated soils may have damaged the plants' root systems, a problem that will restrict growth later in the season.

That possibility concerns Tyler Cooprider, who said three-quarters of their fields were emerged before the flooding. "Right now, everything looks uniformly pukey," he said, of his yellowed, battered corn plants.

Don't despair at yellow plants, which can often bounce back with sunlight and heat, Porter said.

"Yellow isn't the end of the world," she said. "I'd much rather be looking at yellow corn than a situation where seeds are still just sitting there."

She recommended digging up plants and splitting them in half. A healthy plant's center will be white and firm.

See Luce's article, which has a guide for replant decisions, here: http://bit.ly/….

DISEASE-COMPROMISED PLANTS

Plants aren't alone in the field. Rotting diseases such as Pythium and Fusarium thrive in cool, wet soils and prey on slow-growing corn and soybean seedlings.

As you do stand counts, dig up missing or sick-looking plants to check for rotting seeds, discolored seedlings, or decaying roots -- all signs of disease, said Iowa State University Extension plant pathologist Alison Robertson.

Robertson recommends scouting a couple weeks after the flooding. "Dig up the plants, and gently remove the dirt from around the roots and seed," she said. "If its corn, then look at mesocotyl, if its soybeans, the hypocotyl. It should be nice and white if it's healthy."

Pythium is of special concern this season, both Porter and Robertson noted. Certain strains of the Pythium fungus have shown resistance to the common fungicide metalaxyl, found in many seed treatments.

A new fungicide active ingredient from Valent is available in corn and soybeans, called ethaboxam. Read more about it from Burrus Seed here: http://bit.ly/… and DuPont Pioneer here: http://bit.ly/….

For help scouting for disease, see this University of Nebraska article from Extension plant pathologist Tamra Jackson-Ziems: http://bit.ly/….

PRODUCT INJURY

Reports of damage to soybean seedlings from PPO herbicides are beginning to surface, which is not surprising, Porter said. Many growers have used PPO herbicides as pre-emergence residuals in their soybean fields.

"Whenever it is cool and wet, soybeans are slower growing and more apt to get some injury or a little burn," she said.

See pictures of PPO soybean injury from the University of Illinois here: http://bit.ly/….

To differentiate the injury from disease, dig up the plants, Robertson said: "The roots would still be fine." The hypocotyl may show some swelling and reddish discoloration, however, according to the Illinois article.

Another common early season soybean injury is from Bayer's seed treatment, ILeVO. The fungicide active ingredient, fluopyram, can cause some brown discoloration along the edges of the cotyledons, called a "halo effect."

See more on it from Iowa State University here: http://bit.ly/….

Porter isn't expecting this to be prominent this year because the phenomenon requires an ingredient many Midwesterners have been lacking.

"It's a photo reaction, which means you have to have sunlight," she said. "We haven't seen much of that!"

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

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.

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Emily Unglesbee