Ag Weather Forum

Hot days and nights will brand themselves in the collective weather memory for the central U.S. when the last full weekend of August 2024 is brought up. A Sunday, Aug. 25, 2024, bulletin from the NOAA Weather Prediction Center noted: "Temperatures will soar into the 90s to around 100 early this week across the Midwest, which may be the hottest it's been all summer ... Daily high temperature records may be broken." This follows a weekend when temperatures of as much as more than 100 degrees Fahrenheit cooked much of the Plains and the northern Midwest.

This extreme heat is, of course, dangerous for people, livestock and pets. But it's also stressful for crops, with corn in the final stages of filling before ripening and soybeans in their pod-filling stages.

Most corn in the U.S. is now in the R4 or dough stage. At this point, kernels will likely not be lost because of heat, but those kernels can certainly be smaller. A Purdue University article, "Grain Fill Stages in Corn" authored by Dr. Robert Nielsen has this detail:

By dough stage, four embryonic leaves have formed and the kernels have reached about 33% of their mature dry weight. Kernel moisture content is approximately 70% at the beginning of R4. Near the end of R4, some kernels will typically be starting to dent. Kernel abortion is much less likely to occur once kernels have reached early dough stage, but severe stress can continue to affect eventual yield by reducing kernel weight.

The effect of this end-of-August heat calls into question whether corn yields will be able to hit the 183.1 bushels per acre (bpa) projection in the USDA Aug. 12 NASS crop production report. Also, the record projected soybean yield of 53.2 bpa may not be attained due to the drying effect of this heat wave.

To add to the potential for yield impact, the NOAA Climate Prediction Center (CPC) calls for the potential for a rapid onset of drought in the Eastern Corn Belt and the Mississippi Delta during late August and early September. "Prolonged rainfall deficits combined with continued above-normal temperatures results in the potential for rapid onset drought for parts of the Southern Plains and the Ohio, Tennessee, and Mississippi valleys ... Risk for rapid onset drought for portions of the Southern Plains, and the Ohio, Tennessee, and Lower and Middle Mississippi Valley," the CPC noted on Friday, Aug. 23, 2024.

This late August heat wave is in sharp contrast to conditions enjoyed by the U.S. Corn Belt back in August 2004. That year saw corn yields take a leap forward with the national yield coming in at more than 160 bpa for the first time in history (160.4 bpa). That was 18.2 bpa and almost 13% above the previous record the previous year in 2003. But that record year also featured a very cool August with no late-summer heat issue. The NOAA August 2004 U.S. Climate Report had this comment: "August 2004 ranked as the 7th coldest August in the 1895 to present record. The preliminary nationally average temperature was 71.0 degrees F (21.7 deg C), which was 1.8 deg (1.0 deg C) below the long-term mean." Summer temperatures (June-July-August) also averaged just over 71 deg F. In addition, U.S. precipitation in 2004 was above average, meaning a cool and wet summer for corn to completely fill out.

The Purdue University article on the filling stages of corn kernels is available here: Grain Fill Stages in Corn (Purdue University).

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

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