OK, you've got us. No one can find out if they did the right thing by going ahead and planting corn late or by switching to an earlier hybrid, or staying with a fuller-season one, until this particular season plays out. But history can be a powerful guide. Here's a way to determine what you can expect to happen based upon what's happened in the past.
First and foremost, you can expect the hybrid you just panted within the past 10 days or so to mature faster than it would have planted April 30 or May 5. While it may be a downer form the yield sie, it will be positive should the crop wind up in a race against frost to reach physiological maturity this fall. Agronomists define physiological maturity as the point at which the black layer forms in the kernel. That's the time at which materials are no longer able to pass in or out of a corn kernel.
Based on studies by Purdue University's Bob Nielsen and Ohio State University's Peter Thomison, the big change occurs form silking to black layer. There will be some acceleration in the process from planting to silking as well. The total change can amount to about 200 heat units.
Here's what that could mean to you. It's reported in more detail in the 2008 edition of the Purdue University Corn & Soybean Field Guide, published by the Purdue Crop Diagnostic Training Center, led by Corey Gerber. Learn more at: www.agr.purdue.edu/dtc or www.entm.purdue.edu/fieldcropsipm.
Suppose you live in Tipton County, and planted a hybrid on May 31 that normally requires 2,800 heat units to reach maturity. First killing freeze of 28 degrees, the point at which all growth would stop, historically happens in that area on October 23. What's the odds you will get enough heat units to reach maturity? When corn is killed by freeze before it reaches physiological maturity, bad things happen.
The table in the guide that shows accumulation of heat units on average is based upon 30 years, from 1971 through 2000. Using that table, nearly 2,700 heat units accumulate on average from May 30 until October 24. So if the hybrid adjusts and can get by on 2,600 heat units, as research indicates it will, you should be home free. If this phenomenon wasn't so, you would run a much higher risk of suffering damage before the hybrid was fully mature.
Heat units accumulate slowly after October 23, on average. In fact, another 100 units typically won't accumulate in central Indiana between October 24 and the end of November. For all intents and purposes, the season is shutting down at that point.
Here's hoping your late-planted corn knows how to read the manual about speeding up its maturity, which it well, since it's a natural trait, and here's hoping Jack Frost stays away a bit longer this year.