Consequences of Drought and Heat Stress in Corn

Drought took a toll on Missouri crops in 2018, including this corn field in Ray County, near the town of Hardin. (July 2018) ( Tyne Morgan )

Drought, hail, high winds—you name it and somewhere in the U.S. farmers are enduring it. Corn is being inundated with challenges from Mother Nature, here’s what you need to know and how you can set expectations if you have damage.

Much of the western U.S. is enduring at least some level of drought or drought-like conditions. With pollination nearing, or currently happening, for many farmers this could spell trouble.

“Heat and dry weather are not desired weather conditions in the two weeks before or after pollination,” says Mark Licht, Iowa State Extension agronomist. “This four-week time period is finalizing the kernel number per ear.”

Corn water use is at its peak during this time, too, at 0.25 to 0.45 inches per day, he adds. Water is needed to help cool the plant and for silk elongation and filling kernels.

While heat stress and drought stress are different, they often occur simultaneously and can be hard to distinguish. Here are conditions in which heat or drought stress can occur:

  • Temperatures greater than 95 degrees F without moisture stress causes heat stress.
    • Combined with low humidity, silks desiccate
    • Pollen is killed with temps above 100 degrees F, and severely injured over 95 degrees F
  • Moisture stress, or drought stress, is evident when leaves continue to roll and wilt
    • Low moisture slows silk elongation
    • Moisture stress reduced kernel count
    • Continual wilting two weeks prior to silk emergence can reduce yield by 3% to 4% per day; during silk emergence and pollen shed by up to 8% per day; and in the two weeks after pollination 6% per day

drought map