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Corn Watch: Temperature accumulation determines when corn will emerge.

Tom J Bechman 1, Editor, Indiana Prairie Farmer

May 22, 2017

3 Min Read
COOL AND WET, AGAIN! For the second year in a row, rain and cool temps played havoc with early planted corn. This field was planted April 20. The photo was taken May 10.

Yogi Berra, the New York Yankees baseball legend, was known for humorous sayings. One quoted often is: “It’s déjà vu all over again,” which literally means it just happened again — twice. He was a smarter guy than many people thought.

Berra would describe the start of the 2017 growing season as déjà vu all over again! In 2016, late April and early to mid-May wet spells and very cool weather made emergence for corn difficult and inconsistent. Some people replanted. The farmer managing the Crop Watch ’16 field spotted in corn. The same scenario unfolded this spring, with more emphasis on torrential rain and cool, but not cold, weather during the same period.

As you would expect, corn responded the same way, for the most part. Soil type and location in the state were perhaps more factors this year.

Temperature factor
By May 10, corn on well-drained, medium-texture and somewhat poorly drained, medium-texture soils in the Corn Watch ’17 field in central Indiana had emerged. Most plants were yellow with a few other colors sprinkled in, but they were up. The stand looked reasonable and uniform. However, in lower parts of the field, on darker, poorly drained soils — especially where water stood or erosion filled in the planting trench — corn wasn’t up.

Farther north in Benton County, Ind., Purdue University Extension corn specialist Bob Nielsen says one farmer-cooperator planted April 21. At last report on May 10, the crop hadn’t emerged. After checking temperature records and using a website that estimates corn emergence and growth based on accumulation of growing degree days, he wasn’t surprised.

“There hadn’t been enough growing degree days accumulated there to bring it up,” says Nielsen. “Germination and emergence were happening, but at a very slow pace. The seed was doing exactly what it was supposed to do. We know it needs around 125 heat units to emerge. It’s the weather that didn’t cooperate.”  

Corn germination
Just how low can temperatures be when you plant corn? “That depends on if it’s April 20 or May 15,” Nielsen says. “If daily high soil temperatures are in the 50s on May 15, you expect warmer temperatures; you would probably plant. But on April 20, you can’t assume temperatures will warm up soon.

“My first preference as a guideline is to have daily high soil temperatures of 50 degrees F or more if you’re planting. Second, I don’t want daily lows for soil temperature going into the 40s.”

Soil temperature drives when germination and emergence occur, Nielsen emphasizes. If the daily average soil temperature is in the low 50s, it may take 21 days or more for emergence. If soil temperatures are in the 60s, which are more likely in mid- to late May, emergence may happen in a week.

If your corn took roughly three weeks to emerge, be on the lookout for seedling blights, Nielsen says. Many seed-coated fungicides begin breaking down at about three weeks.   

Seed Genetics-Direct, Washington Courthouse, Ohio, sponsors Corn Watch ’17.

About the Author(s)

Tom J Bechman 1

Editor, Indiana Prairie Farmer

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