Pro Farmer Editors
Purdue University agronomist Bob Nielsen says late-planted corn in Indiana faces obstacles and needs more calendar days to reach physiological maturity. He notes as of July 27, Indiana's corn silking progress was 1.5 to 2 weeks behind the 5-year average and closely resembles the progress of the 2002 and 2003 crops.
"If the comparison to those years holds through to maturity, quite a bit of Indiana's corn crop may mature from late September through mid-October," he says. "That prospect is the reason why folks are looking to the calendar and praying that the first killing fall freeze does not come early this year."
Based on climatological historical normals for Indiana (National Climatic Data Center, 2008), a killing fall freeze occurs 10% of the time, on average, by the 10th of October in Indiana and ranges from as early as the first week of October to the last week of October depending on the area of the state. Fifty percent of the time, on average, a killing frost freeze occurs by the 26th of October in Indiana and ranges from as early as mid-October to as late as mid-November.
"Given that perspective on fall freeze dates, what can be said about the likelihood that a given field of corn will mature safely (physiological maturity, kernel black layer) prior to a killing freeze? One of the simplest means by which to estimate maturity date may be in terms of number of days after silking," he says. "Results from earlier research on corn development with delayed planting suggest that corn planted in mid- to late-June in Indiana and Ohio will typically mature from 68 to 71 days after silking. The number of days from silking to maturity increases with later-planted corn primarily because growing degree day (GDD) accumulation per day decreases dramatically toward late summer and early fall and so it simply requires more calendar days for a late-silking crop to accumulate a minimum number of GDDs to reach physiological maturity."
"These results do not bode well for late-planted corn that silks during the first or second week of August, because they suggest that physiological maturity of such late-silking corn may not occur until mid- to late-October where the risks of a killing fall freeze increase," he adds. "Furthermore, grain of late-maturing crops will not dry as quickly in the field prior to harvest because of the naturally cooler temperatures of that time of the year."