The common line is that late planting causes hybrids to speed up and mature about 200 growing degree day units faster. That's still true, but hold that thought. There are other factors influencing late-season maturity these days.
Is it a GMO or non-GMO hybrid? If it's a GMO hybrid, expect it to stay healthier and dry down slower, just because its's healthier, at least compared to its genetic non-GMO counterpart or to a hybrid of the same maturity range. In almost all situations, strong plant health is a good thing. But if you're going to be forced into planting late and worried about corn drying down next fall, especially if you have to sell it our of the field, that might not be a good thing.
Dave Nanda saw a vivid example of that a few yeas ago on the Corn Illustrated plots, then sponsored by Indiana Prairie Farmer. A GMO and non-GMO hybrid were in the same field, both planted the last week of May. The non-GMO hybrid stayed healthier, and was up to two points wetter when harvested on the same day in late October.
It's just another factor to consider if you're switching out hybrids to get something earlier or different because of the rain delays, Nanda notes. For example, if you're now afraid of corn borer because of late planting, recognize that if you switch to a GMO hybrid, it may in fact stay healthier longer, which is good, but dry down slower next fall as it stays green longer, which may not be such a good thing.
Purdue University and Ohio State University researchers several years ago did testing to conclude that the same hybrid planted up to 30 days apart requires less heat units to mature planted later. For example, if hybrid A requires 2,800 heat units to mature planted on May 1, then it only requires 2,600 heat units to reach the same point in maturity planted on May 30. That's the result of a 30-day delay in planting.
The conclusion from their study was that full-season hybrids for the area can be planted later than once thought and still mature prior to the date of a typical killing freeze, depending upon the actual date of planting and accumulation of heat units at that location in that particular year.