Corn sweat (noun): a process where corn plants pull water from the soil and release water vapor into the air through their leaves, also known as evapotranspiration.
This is a natural process for the corn plant and is most common for corn grown in the Midwest.
Corn sweat process
The transition of water from the corn plant to the atmosphere occurs through tiny pores, called stomata, in the corn leaves in addition to other surfaces on the corn plant. The stomata open to take in carbon dioxide for plant growth and release water to cool the plant down.
Water loss from the soil, called evaporation, and water loss from the crop, called transpiration, make up the entire process, called evapotranspiration.
When does corn sweat typically happen?
As peak corn growth occurs in top producing corn states during the hot, summer months in the United States, corn sweat is typically felt during the same time. Corn sweat tends to peak in July and early August in the weeks after the crop reaches the tasseling stage.
Tasseling and flowering stages are the peak of water use in corn. From those stages, water use only decreases and suggests that corn sweat should also decrease at that time as the crop approaches maturity
Higher humidity
When corn sweat occurs across millions of acres of corn crop and adds huge amounts of moisture to the air, humidity increases and makes hot summer days feel muggier and warmer than they already are, especially when you are walking fields to detassel corn or crop scouting for the season.
According to Duane Friend, University of Illinois Extension energy and environmental stewardship educator, corn can add up to 4,000 gallons of water vapor to the atmosphere per acre per day at its peak.
Therefore, corn sweat affects conditions by increasing the “real feel” temperatures even if the actual temperature is mild and increases chances for higher nighttime temperatures with increased moisture in the atmosphere.
All in all, the term “corn sweat” is more of a “Midwestern slang” name for the process of evapotranspiration.