URBANA, Ill. - With a massive heat dome settled over the Midwestern Corn Belt, many farmers are starting to stress over the possibility of crop damage and yield loss. But are the crops as stressed as the farmers?

“As high temperatures continue and rainfall remains scarce, many Illinois producers are getting concerned about prospects for the 2024 crops,” reported Emerson Nafziger and Giovani Preza Fontes from the Department of Crop Sciences at the University of Illinois on June 21. “Crop condition has dropped some, but is much higher than it was at this time in 2023, before rains turned things around and yields ended up high.”

In their article for The Bulletin, “Stress and the 2024 corn and soybean crops,” the crop specialists cautioned that early-planted corn is likely more at risk for damage than later-planted varieties and soybeans at this point in time. Field surveys have shown that corn plant stems have elongated more slowly than normal, probably due to less available water. Precipitation will quickly restore rapid stem elongation in such fields, according to the authors, but plants may end up shorter than normal.

“Visible stress that continues means decreasing soil water, lower photosynthesis, and some additional loss of leaf integrity. Lower stem diameter is normal, but there is little brace root development. Lower leaves also have an unusual, and unhealthy-looking, color. It is not clear that these will revive to become productive even if rains return. If upper leaf expansion is limited as well, canopies may remain incomplete and kernel numbers and grain-filling rates may be lower as a result,” Nafziger and Preza opined. 

“We think there is enough water in the soil to maintain the crop’s yield potential for a week or two still, but that will come at the expense of lower daily productivity as leaves curl earlier as soils dry out.” 

Late-planted corn faces its own risks, though the researchers noted that plants they observed had emerged well and appeared to be growing well, with little afternoon leaf-curling. However, “while less stress is a good thing, having so much of their growth and yield potential still to develop represents some risk to yield in late-planted fields,” according to the U of I crop advisors. 

As for soybeans, “the soybean crop has reached stage V8-R2, with 8 expanded trifoliolate leaves and flowers at most developed nodes. These plants have a little less leaf area than if they had had a more plentiful water supply, but there is no indication that node and pod numbers have been compromised,” Nafziger and Preza commented. 

“Although late planting is something we’d prefer never to see, we know that today’s corn hybrids and soybean varieties have remarkable ability to come back from stress effects in the first half of the season to yield well. There is no indication that we need to apply more and different inputs than we normally would in order to enable such recovery. With crop insurance there to prevent catastrophic loss in case stress continues through the rest of the season, we can proceed with normal attention to the crop through the rest of the season, and deal with issues as they arise.”

University of Illinois Extension crop advisors across central Illinois confirmed the researchers’ assessment of the 2024 corn and soybean crops during the June heat wave. 

“Like much of the state, in LaSalle County it has been hot with only one day in the past week having some scattered showers,” reported Emily Hansen, commercial agriculture educator for the LaSalle County Extension. “Overall, crops are still looking good, but the soil is starting to dry out a bit on top.  Corn at the IVCC (Ill. Valley Community College) research and demonstration plots is at V5, and soy is at V2/3 (both planted May 20). Later planted or replanted crops in LaSalle County are at similar maturity, but earlier planted corn is reaching V10 – V11 stage and some earlier soy is getting close to R1.”

Reagan Tibbs, Extension commercial agriculture educator in Logan County, added: “High temperatures have entered the area and are putting pressure on crops in Logan, Menard, and Sangamon counties. While there has not been a major rainfall event for some time, and the topsoil moisture supply is lower, there is still moisture down further in the root zone that is allowing crops to receive water. 

“The forecast shows no break in the heat anytime soon, and chances for rain each day remain in flux. Most of the crops still appear to be healthy and have yet to exhibit signs of heat stress. There are some crops, especially ones in sandier soils, that are beginning to exhibit signs of stress.”

Though crops in the Midwestern Corn Belt may emerge from under the heat dome unscathed, the prospect for crop stress in the South, however, is higher as silking — the first stage of corn’s reproductive period – has started. 

“June is a bad time for a heat wave for corn across the southern United States,” said Brad Rippey, a meteorologist with the U.S. Department of Agriculture. “That is something we’ll have to watch.”

Rippey noted that Midwest crops have yet to reach the reproductive stage, making it more likely they’ll fare better during the prolonged heat wave. “If it were three or four weeks later, there would be significant concerns because corn would be moving into reproduction and some of the earlier planted soybeans would also be starting to bloom,” he said.

(Recommended reading: Nafziger, E., G. Fontes. “Stress and the 2024 corn and soybean crops.” Department of Crop Sciences, University of Illinois at Urbana-Champaign, June 21, 2024)