Weather Whiplash

Heat Wave Stresses Poorly Rooted Corn Crop

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
Connect with Emily:
The state of Nebraska put its support behind a rewrite of the waters of the United States rule. (DTN file photo)

ROCKVILLE, Md. (DTN) -- If you're experiencing a little whiplash right now, you're not alone.

Less than two weeks ago, Illinois farmer John Werries was patching in soybeans over 500 acres, thanks to one of the wettest months of May on record.

This week, he's watching his corn roll into spiky little pineapple leaves.

"It is hard to believe after what we have been through with the heavy rains," he told DTN. "We replanted almost 50 acres of drowned-out spots in corn, and now we have corn rolling on even the best soil."

For others, the recent wave of 90-plus-degree temperatures in the Midwest and Northeast has been a healing balm to soggy, sun-starved crops. "The low humidity and warmer weather were welcomed here in northeast Ohio and northwest Pennsylvania the last few days," said Ohio farmer Loren Hopkins.

The minor heat wave that rolled across much of the Midwest this past weekend was not as hot as anticipated, said DTN Senior Ag Meteorologist Bryce Anderson. "The actual temperature value did not get quite as hot as the forecast indicated late last week; however, strong winds did cause some stress to crops in much of the Midwest," he noted.

June heat isn't unusual and crops normally pull through it, agronomists noted. However, many corn stands are suffering from restricted root systems that will hamper their ability to bounce back this year.


Many soybean plants are still small enough to dodge damage from heat stress, agronomists told DTN. Corn plants were the biggest cause for concern for farmers this week, as leaves rolled up tightly across the Midwest.

Corn rolling isn't an automatic sign of trouble. The spiked leaves are the corn plant's first line of defense against hot, dry air causing more evapotranspiration than normal, said Jack Hardwick, an independent agronomy crop consultant in Illinois.

Corn in the V8 to V10 stage is usually equipped to handle about 0.2 inch of moisture of evapotranspiration. When temperatures soar beyond 90 degrees Fahrenheit, accompanied by low humidity and lots of wind, that rate doubles, Hardwick noted.

"So the corn is rolling because it senses that the leaf surface is dryer than it should be (due to low humidity/wind/sun) and also because some plants don't have root systems built to handle a 0.4 inch-0.5 inch water pull during the day," he told DTN in an email.

The same phenomenon was spotted last year at this time, when a heat wave in June stressed cornfields that went on to produce record yields in many states.

So why worry?

Corn and soybeans aren't in the same condition as they were in 2016, agronomists noted.

There are a lot of restricted corn root systems in the Corn Belt right now, said DuPont Pioneer agronomist Matt Montgomery.

"Roots had to grow in a low-oxygen environment, which makes them shallow," he said of the saturated soils this spring.

Sidewall compaction from working wet ground this spring is another major root inhibitor this year, agronomists and farmers noted.

"Heat and no rain have turned compacted soils into concrete and is putting any emerged crop from April or May planting under stress," said Indiana farmer Randal Plummer.

"If the corn root system is restricted, there's going to be a bigger injury from heat stress," noted Iowa State University Extension field specialist Joel DeJong. "Stress at this stage could slightly reduce the number of rows on an ear," he said of the V6-V8 corn plants in northwest Iowa where he works.

"Playing defense is a good thing, but we don't want it to endure for long because when the plant rolls, very little vegetative growth happens while the plant keeps aging," added Hardwick.

Smaller plants could set the stage for lower yield later in the season, but the corn crop still has plenty of time to recover before the most critical and heat-sensitive stage of pollination, agronomists said.


Many soils have abundant subsoil moisture, thanks to the wet spring. But until root systems can expand and reach it, stressed crops could continue to suffer, Montgomery said.

"We just need to get the topsoil wetted down so the moisture can make contact with the root systems in place now," he said.

Many parts of the Midwest may be in luck this week, Anderson said.

"This week does look rainier than the forecast indicated last week," he said. "Our DTN forecast model has rain of 0.5 inch to 1.5 inches, with locally heavier amounts, for totals in the Midwest during the next seven days. Northern Plains areas will also get some rainfall, probably in the 0.5- to 1.0-inch range."

Any amount is welcome in the Dakotas, where drought has been building steadily for weeks, noted South Dakota State Extension crop production associate Jonathan Kleinjan.

"In central South Dakota, many growers are baling up a lot of their winter wheat or spraying it out," he said. "It's bad out there."

Established corn and soybean stands are small enough to recover, but the heat has probably already reduced late-planted stands, Kleinjan added.

"We're not going to have near the crop in South Dakota that we did last year because of the combination of late planting and reduced stands and dry weather," he said.

(See a DTN story on the drought conditions in the Dakotas here:…)

For more information on heat stress effects on corn and soybeans, see this industry summary of academic articles:….

Emily Unglesbee can be reached at

Follow Emily Unglesbee on Twitter @Emily_Unglesbee


Emily Unglesbee