Ag Weather Forum

Friday, June 20, marked the summer solstice -- and with that, the beginning of this year's astronomical summer season. Almost in lockstep, extreme heat warnings went into effect for much of the central and eastern U.S. The western Midwest got the first helping of this heat wave, with the eastern Midwest and the Atlantic seaboard in line for their share of this hot spell as the week goes on. This heat wave will be relatively short-lived. Still, as DTN Ag Meteorologist John Baranick noted in a post describing the build-up of this event, "... its intensity will remind us that it is indeed summertime in the U.S."

This heat wave brings to mind how extreme heat can impact the corn crop's performance. Corn can handle some heat, but not too much. Even though this extreme heat is happening before most corn plants have begun the pollination phase, the heat still takes a toll on the condition of plants, and the subsequent yield at harvest.

The impact of heat waves like the one we're seeing on corn production are covered in an article by Dr. Mark Jeschke, agronomy manager at Pioneer Hi-Bred International (subsidiary of Corteva). Jeschke's article, titled "High Temperatures Increase Water Stress in Corn," makes these primary key points:

-- Higher temperatures cause the transpiration rate of plants to increase, placing a greater demand on soil water supply and accelerating the onset of drought stress.

-- The increased water demand under extreme heat is substantial -- raising temperature from 80 to 95 degrees Fahrenheit (27 to 35 degrees Celsius) causes water demand to double.

-- Corn plants respond to water stress by closing their stomates, which helps preserve water but also reduces intake of carbon dioxide (CO2) needed for photosynthesis.

The timing of this heat wave is prior to the pollination phase of most corn plants, which is favorable from the standpoint of corn still being in its vegetative, pre-pollination phase. Writing in the Purdue University agronomy website, Dan Quinn noted, "The good news is that corn originated from a tropical grass and has been observed to withstand temperatures upwards of 112-degrees F for short periods ... Therefore, temperatures in the mid-90s during the afternoon typically do not impact corn photosynthetic capacity and yield if soil moisture is adequate."

A review of soil moisture conditions over the primary U.S. crop areas shows much of the Midwest with near-normal moisture; wet conditions in the southeastern Plains, southern Midwest and Delta; and drier conditions in the Central and Northern Plains. Many of the drier areas are also where irrigation is extensive, which means the water systems may be needed to help maintain soil moisture and cool down the plant canopy.

This heat wave follows a spring season that was a warm one. USDA's Weekly Weather and Crop Bulletin summarized conditions this way: "On the strength of consistently above-normal temperatures, featuring the sixth-warmest March, 14th-warmest April, and 26th-warmest May, the continental U.S. experienced its second-warmest spring on record." So, with that scenario, this week's heat wave is probably not a surprise. But it does jar the nerves thinking about crop conditions for the rest of the season.

Bryce Anderson can be reached at bryce.anderson@dtn.com

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