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Slow Corn Drydown in 2023 – Why?

I have heard local reports that corn is wetter than normal this year, causing bottlenecks in handling and drying, and delays to harvest operations. Some have surmised that haze from the Canadian wildfires may be to blame. A Purdue expert doesn’t seem to buy that theory.

Dr. R.L. (Bob) Nielsen, professor emeritus of Agronomy at Purdue University, is the author and curator of content at his Chat ‘n Chew Café website.

“Some scuttlebutt down at the Chat 'n Chew Cafe suggests both the slow maturation and drydown in the field this fall were caused by all those smoky hazy days back in early to mid-summer, courtesy of the wild fires in parts of Canada,” said Nielsen. “I don't buy into that theory.” He said that while it may be true that smoky haze (or cloudy haze for that matter) influences plant photosynthesis (and thus potentially grain yield), it does not DIRECTLY influence the rate of plant development (i.e., how fast plants mature).

“Rather, it is primarily temperature that drives the rate of plant development (Nielsen, 2020),” he said. “The warmer it is, the faster corn progresses through its growth stages. The cooler it is, the more slowly corn progresses.” He added that the smoky days may have INDIRECTLY contributed to the slower maturity if they contributed to cooler temperatures. However, even if that was true, the cooler temperatures did not occur ONLY on those smoky days.

Nielsen said the climatological evidence suggests that the 2023 growing season was generally cooler than normal throughout and not just due to smoky days. He referenced a corn Growing Degree Day (GDD) calculator on the Useful to Useable website,

I plugged a few hypothetical parameters into the tool to compare this year to the last 2 growing seasons in Whitley County. Using a 108-day hybrid planted about any date in May, we are behind 2021 and 2022 in Growing Degree Days, just below the twenty-year average (1991-2020). You can use the tool with your farm’s specific numbers to compare to prior years.

“Cooler temperatures in mid-June put us behind normal early on and then around mid-Aug cooler than normal temperatures again expanded that deviation further,” he said. “Continued cooler than normal weather…since black layer development has further slowed the in-field drying of the grain.”

“The bottom line that one can derive from the preceding rambling thoughts is that the slow grain drydown in parts of Indiana in 2023 is primarily due to a combination of later than desired planting plus cooler than normal temperatures throughout the whole season and not due to the relatively few number of smoky hazy days we experienced,” said Nielsen. “In fact, about 50% of Indiana's corn crop in 2023 was planted after mid-May so it may not be surprising that so many farmers are complaining about this issue.”

Find Nielsen’s original article at

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