Corn sweat and sticky summer heat
Published 12:30 am Tuesday, August 11, 2026
High temperatures and high humidity coinciding with one of corn’s most critical growth stages results in a condition many refer to as “corn sweat.”
University of Missouri Extension State Climatologist Zachary Leasor said corn sweat is a colloquial term for transpiration, the natural process of corn plants pulling water through their roots and releasing vapor, mostly through the stomata of their leaves, into the atmosphere.
Combined with evaporation of water from the ground, the total process of evapotranspiration can make already-humid air even more humid in areas with widespread crop production.
Corn sweat generally happens in late July to early August when crops have reached full canopy development.
“At this time, crops and other vegetation are maximizing their water use primarily to cope with the heat and cool their foliage,” MU Extension soybean agronomy specialist Andre Reis said.
Leasor said research has found that crop transpiration can increase surface-level humidity and may play a role in complex atmospheric processes such as thunderstorm development.
“However, it remains difficult to accurately quantify how much of the humidity may be due to an additional contribution of the crop transpiration, and how far this humidity can move across a region or vertically in the atmosphere before being mixed with atmospheric moisture from other sources,” he said.
Corn leafhopper
Corn leafhoppers have been confirmed in five Missouri counties – Boone, Barton, Christian, Lawrence and Cooper.
First detections in 2026 occurred about three weeks earlier than in 2025.
The corn leafhopper is about ⅛-inch long, about the size of a grain of rice, with a yellow to tan body color. Adults are characterized by two small black spots surrounded by lighter-colored halos located between the eyes, with no additional markings on the head or body.
Research outside the U.S. has shown that corn plants are most susceptible to infection by corn stunt pathogens, which corn leafhoppers can carry, during the vegetative growth stages, from emergency through tasseling.
Corn stunt symptoms appear one to eight weeks after inoculation. Most common symptoms include yellow streaks on the base of infected leaves and yellowing or reddening of leaf tips.
Management is complex, and once plants are infected, damage is irreversible, MU Extension state field crops and forage entomologist Ivair Valmorbida said. The earlier the infection, the greater the damage.
“At this time of year, scout efforts should focus on late-planted corn. If present, an insecticide application may be warranted if corn has not reached the R1 growth stage,” he said.
Missouri 4-H Building
A landmark on the Missouri State Fairgrounds begins a new chapter this week.
A ribbon-cutting ceremony will take place at 2:30 p.m. Thursday for the restored historic Missouri 4-H Building.
“For more than a century, it has served as a gathering place where young people have showcased their achievements, built lifelong friendships and celebrated the values of Missouri 4-H,” Missouri 4-H Foundation Executive Director Rachel Augustine said.
The restoration project preserves the building’s historic character while making improvements that will allow it to continue serving Missouri 4-H youth and visitors for years to come.
The project was made possible through fundraising efforts led by the foundation in partnership with the Missouri State Fair, along with the generosity of donors and supporters from across the state, Augustine said.
The building remains one of the most recognizable on the fairgrounds and continues to serve as a hub for Missouri 4-H activities during the Missouri State Fair.
