Compromised Corn Ahead

Watch for These Six Corn Problems in Wet or Late-Planted Fields

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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These corn leaves rolling in central Illinois this week are showing the effects of the wet, challenging planting season of 2019. (DTN photo by Pamela Smith)

ROCKVILLE, Md. (DTN) -- Rather like the old Bible verse, some cornfields are starting to suffer for the sins of their planters.

"As you might imagine, we're seeing a hodgepodge of problems, since so much of the corn was put in wet," said Purdue University corn agronomist Bob Nielsen. Between soil compaction and saturated soils, many root systems have been compromised, and disease and pollination concerns lurk.

Here's a quick look at the six most likely "sins" to surface in your late- or wet-planted cornfield this summer:

PINEAPPLE LEAVES

In many fields, the soil is far from droughty, but corn plants are saying otherwise.

"There's a lot of tillage compaction or planter compaction in the furrow in some of these fields, and with this hot weather over the past week, there's been a lot of fields with leaves rolling, indicating drought stress when technically soil moisture is probably adequate," Nielsen said.

At issue are constricted root systems that aren't able to tap into moisture deeper in the soil profile. If these fields get more rain in the weeks to come -- which looks likely for many -- the rolling may stop. But plants that head into drier conditions will not recover as easily.

"Only time will tell how serious leaf rolling will be," Nielsen said. See more on corn rolling from DTN here: https://www.dtnpf.com/…

ROOTLESS OR FLOPPY CORN SYNDROME

When young corn plants start developing their root system, the roots that branch out from the nodes at the crown root are especially vulnerable to hot, dry soils.

"If it's too dry there in the upper 2 to 3 inches of the soil, those young roots just shrivel up and die," Nielsen explained. "In extreme cases, those young corn plants are surviving solely on the connection to the seed and the roots that come down from the seed. A good, strong wind can flop them over and sometimes result in death or, at a minimum, gooseneck corn and stunted corn."

The sudden collapse of the plant can come as a surprise to growers, since the aboveground corn plant can continue to look fully healthy, thanks to its surviving root system.

The condition most often occurs in young, knee-high corn plants that are still actively developing their nodal roots. Other risk factors include shallow planting, furrow erosion from heavy rains after planting, soil compaction and open seed slots -- all of which occurred in the wet, rushed and difficult planting season of 2019, Nielsen added.

"Unfortunately, for this problem, there's nothing a grower can do short of irrigation, if they have it," Nielsen noted. "Otherwise, they're just dependent on rainfall to help those roots grow deeper."

See more on this syndrome here: https://www.agry.purdue.edu/…

RAPID GROWTH SYNDROME

If you've spotted strange-looking whorls and yellow leaves in your cornfield, don't panic. You're probably seeing the result of corn plants growing rapidly after a prolonged period of slow development in cool, cloudy conditions.

Rapid growth syndrome, or twisted whorl syndrome, is a common sight so far in Indiana, as corn plants are finally getting the heat and sun they need to mature quickly, Nielsen said. For reasons not fully understood by scientists, the emerging leaves get stuck and don't unfold properly, which causes a tightened, twisted whorl.

Once the twisted whorl releases its grip and unfurls, some of the trapped leaves may appear yellow for a few days, due to the lack of sunlight they experienced.

"The good news with this phenomenon is it's mostly a cosmetic thing, and rarely does it lead to any long-lasting negative issues for the plant," Nielsen said. "But, boy when it shows up, it certainly catches your eye."

Read more about this phenomenon here: https://www.agry.purdue.edu/…

CRAZY DISEASE LURKING

Growers who had corn in ponded fields should brace for some strange-looking tassels come pollination, Nielsen warned.

Flooded corn is especially susceptible to a disease called crazy top, which has spores than can swim through pooled water to infect the plant. The infected plants usually go undetected until they put on tassels and things get ... well, crazy.

"Later on, when the tassels come out, they are just these giant masses of leaves," explained Nielsen. The deformed tassels can be huge and strange-looking, which inspires the disease's name. Most importantly, however, they are usually barren and will not produce a healthy ear, adds Iowa State University plant pathologist Alison Robertson.

That plant can also serve as a source of inoculum for the years to come, she noted in a university newsletter.

Read more here: https://crops.extension.iastate.edu/…

POOR POLLINATION RISKS

Many growers planted their corn far later than normal, and as a result, the nation's crop is only just beginning to silk. For Indiana growers, the majority of fields will not pollinate until the last two weeks of July and the first week of August -- among the hottest days of the summer, Nielsen said.

"This is, of course, one of the reasons we don't like to see late planting," he noted. "If that heat is accompanied by inadequate rainfall, the combination of heat and dryness will interfere with pollination and can lead to failed pollination or immediate abortion of newly pollinated kernels."

The situation leaves corn growers with uncertainties about yield potential in fields already compromised by late planting, he noted.

GREEN SNAP

The dreaded phenomenon called green snap can occur any year, but it does seem to be related to rapid growth occurring shortly before pollination, which many cornfields are experiencing right now, Nielsen noted.

An important polymer called lignin is responsible for the tough, woody outer ring of a corn stalk, which keeps it strong and upright. During rapid periods of growth prior to pollination, the corn plant grows faster than the plant can pack on lignin. "The lignification of that outer portion of the stalk doesn't keep up with the vertical growth of the stalk, so you have a thinner, weaker rind around the outer circumference, especially at the stalk nodes -- that's where green snap occurs," Nielsen explained.

Until the lignin deposition catches up, corn plants are very vulnerable to snapping over during strong windstorms, which are a common feature of summer in the Great Plains and Midwest. The snapped plant cannot recover and that yield is lost to the grower.

Read more here: https://www.wyffels.com/…

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

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(PS/AG)

Emily Unglesbee