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For many cornfields, race to finish line looms

Corn Illustrated: Will this year’s crop mature in time? What’s on the line for fields that don’t make it?

Tom J Bechman 1, Editor, Indiana Prairie Farmer

August 13, 2019

3 Min Read
RACE THE CALENDAR: The corn tasseling on the left was planted May 21. The corn yet to tassel was planted June 3 and tasseled during the first week of August. Will these fields mature in time this fall?

The most common observation among farmers when the Indiana State Fair opened Aug. 2 was “my corn looks good — if it were July 2 instead of Aug. 2.” Unfortunately, it was Aug. 2; the nights were already getting longer and the days shorter, day by day. That sets up the two most asked questions at the fair: Will corn mature before a killing freeze? What happens if it doesn’t make it?

Here’s a closer look at each question. The Purdue University Corn and Soybean Field Guide, compiled by Corey Gerber, director of the Purdue Crop Diagnostic Training and Research Center, contains information used in these examples.

Run the race

Will corn mature in time? The Purdue guide notes that if you planted May 2, there are still 2,992 growing degree days left to accumulate by Oct. 10 in a “normal year” in central Indiana. The GDD table is based on data from 1971 through 2010. That number can vary a couple of hundred GDDs either way, depending on where you live in the state.

Suppose you planted May 23 in central Indiana. Now corn should have 2,725 GDDs remaining in that elusive normal year. Planting June 6, a common planting date this year, leaves 2,498 days. Planting June 13, the expected GDD total before Oct. 10 is 2,359.

Suppose your hybrid needs 2,600 GDDs after planting to reach black layer and be safe from frost. If you planted May 2 or even May 23, it appears your crop would be safe. If planted June 6 or June 13, it might come up short.

There is a caveat, however. Purdue’s Bob Nielsen says the same hybrid planted late can mature in about 200 fewer GDDs. So, if it now only needs 2,400 GDDs to reach black layer, it might make it by Oct. 10, except for the mid-June planting date.

Remember, though, that black layer averages 30% to 32% moisture, depending upon the hybrid.

Truth or consequences

What if the crop dies due to freeze, disease or some other factor before kernels reach black layer? What do you stand to lose?

According to the guide, based on long-standing research, if corn leaves die in the soft dough stage, yield loss could be as high as 35%. If the whole plant dies, it could be 55%. Grain moisture would be 65%. At full dent, potential yield loss would be 27% and 41%, respectively, with moisture at 55%.

If the milk line is halfway down the kernel, yield losses could be 6% and 12%, respectively. The moisture of corn would still be around 40%.

To avoid yield loss, corn needs to reach physiological maturity, or black layer. The table in the Purdue guide used to estimate potential yield losses and grain moisture content says grain moisture at black layer could still be 33%.

What’s the bottom line? Some fields will make it unless a killing frost comes disastrously early. Some fields may make it, but with little time to spare. Moisture levels could be high. If you have very late-planted fields, pray for a late frost!

About the Author(s)

Tom J Bechman 1

Editor, Indiana Prairie Farmer

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