Scrub Hub: What is corn sweat? And does it make our Midwest summers muggy?

During the summer, the Midwest can experience some serious humidity. That’s nothing new.

But have you ever thought about where a lot of that extra moisture in the air comes from?

The answer might surprise you: Look no further than the acres upon acres of corn and soy fields across Indiana and our neighboring states.

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You’ve probably heard of the ‘meat sweats’ — the phenomenon of intense perspiration after eating a particularly meaty meal. But what about corn sweat, does that ring a bell?

Despite the similar names, it has nothing to do with eating too much corn.

For this next edition of the Scrub Hub, as Hoosier farmers continue the annual march toward harvest time, we will look at the question of what is corn sweat and what does that mean for Indiana and the Midwest?

To answer that question, we looked at the research and spoke with a crop expert to understand this sensation.

Short answer: The corns way of cooling itself down

So we know what corn sweat is not — I mean, can you really ever eat enough sweet corn when it’s in peak season?

It actually is just what it sounds like: Corn that is sweating, or releasing excess moisture. And just like us, the plants do it to cool themselves down.

Similar to how a person breathes, plants exhale water into the atmosphere through a process called evapotranspiration (otherwise known as corn sweat).

Across the Midwest as well as into some of the Plains states, the crops draw moisture from the ground through their roots into their stems, leaves and the produce. The corn plants then shed that water during hot days as it evaporates from tiny pores in their leaves and goes into the surrounding air.

“It’s just the way the plant is going to cool itself down,” said Darcy Telenko, an extension field crop pathologist with Purdue University, “by opening its stomates and releasing water.”

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While Telenko understands the science and the process of what’s happening, the term “corn sweat” was new to her.

And it’s not just corn, soybeans do the same thing as well as other crops. Trees, too.

“All the plants are sweating if you think of it that way,” Telenko said, it just depends on the temperature and how much moisture the plants have.

Long answer: Enough corn sweat to fill a swimming pool

The impacts of all that “sweat” and the excess moisture is not insignificant.

One acre of corn can release 4,000 gallons of water per day, according to research, which is enough to fill a residential swimming pool in less than a week.

Now multiply that by the more than five million acres each of corn and soy in Indiana, and the many more millions of crop acres across the Midwest and corn belt region.

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Hotter conditions lead to higher rates of evapotranspiration as the plants try to cool down — that means more humidity enters the air when it’s already particularly hot out. That causes a higher heat index, which is measure of how hot it feels when taking humidity into account.

That can make heatwaves not only oppressive and uncomfortable, but also dangerous.

A heat index between 80 to 90 degrees Fahrenheit can lead to fatigue with physical activity or prolonged exposure. Over 90 degrees can lead to heat cramps, heat exhaustion or even heat stroke.

Central Indiana has seen several days this summer with heat indices as high as 100 or 110 degrees Fahrenheit.

The number of extreme heat days continue to grow, largely the result of climate change, according to research out of Purdue University. The number of days over 95 degrees could double by mid-century, the Climate Change Research Center has shown.

The effects of corn sweat are strongest in the center of a field — it can raise the temperature over that field by as much as five to 10 degrees. Still, a person doesn’t have to be standing in that field to feel the heat, the moisture will carry on the wind and can blanket a region.

While the rate of evapotranspiration can change with the temperature, the process peaks when corn reaches its “tasseling” phase. That is when the corn is at its maximum height, begins to sprout and pops a crown of thin spikes.

That phase usually begins around mid-July, or roughly 80 to 90 days after planting, and lasts through August. Humidity levels can increase in the span of just a week or two once the corn reaches that point.

Not only can it be muggier during the day, but the corn sweat and extra moisture can make it slower for the air to cool down overnight. That leaves little respite from the heat for both the crops and communities in the region.

The added moisture also can give a little more juice for summer showers and storms, making them more intense.

Still, if crops are parched from drought — as many pockets across the region, including here in Indiana, have been this summer — they won’t release as much moisture, Telenko said. They will hold on to what they can and need to grow.

“Corn sweat isn’t going to lead to any yield losses,” for farmers and the crops, Telenko said. Still, they have to keep an eye on how much moisture is hanging around in the canopy of the corn and or other crops because if the leaves stay damp for too long, it could open them up to diseases.

Corn sweat by no means is the only culprit contributing to our muggy Midwestern summers. There are also the trees and bodies of water, for example, releasing moisture into the air. But it certainly is a factor — and likely one you've never considered or even heard of before reading this.

So next time you hear the weather person report what seems like an implausible amount of humidity in the air, or it feels like you’re walking through a wall of thick and heavy air, now you’ll know it’s just a little sweat. Corn sweat, that is.

If you have more questions about corn sweat, other impacts from crops or any other topics, let us know!

You can ask us by submitting a question through our Google form below. Can’t see the form? Click here.

Call IndyStar reporter Sarah Bowman at 317-444-6129 or email at sarah.bowman@indystar.com. Follow her on Twitter and Facebook: @IndyStarSarah. Connect with IndyStar’s environmental reporters: Join The Scrub on Facebook.

IndyStar's environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.

This article originally appeared on Indianapolis Star: 'Corn sweat,' Midwest muggy summers, climate change, change humidity