So July and the first half of August were cooler and drier than normal. It turned very hot the last half of August, with little or no rain. The National Weather Service weekly drought monitor map at the end of August showed Iowa had returned to drought conditions. The entire state on August 30 was rated abnormally dry and one-fourth of the state was in severe drought.
Iowa has wide range of planting dates and variable growing conditions in 2013
"Corn is a heat-unit based crop, that's the way it grows and develops," Elmore told folks at the Aug. 30 field day at Ames. "The extreme heat we've had the past two weeks is speeding up maturity. The corn crop is going through its development stages now faster than it normally does because of the heat we've received the last half of August."
But corn planting this year stretched out for almost two months starting in late April and continuing through June. As a result the pollination period was also spread out. July 28 was a key date for this year's corn crop. That's when 50% of Iowa's corn crop silked this year. Yet, some fields in Iowa were just starting to tassel in mid-August.
Corn needs about 60 days from silking date to when it becomes mature, says Elmore. When it reaches maturity corn is safe from frost. Corn will form a black layer in the tip of the kernel soon after it's reached physiological maturity. Looking at this year's situation, fields that silked and pollinated in mid-to-late August won't be safe until mid-to-late October.
Watch the milk line forming on corn kernels, to give you an idea of where your crop is now in terms of maturity
At the end of his presentation at the August 30 field day, Elmore gave people a printed handout. It had a handy table to help tell where your corn is in terms of maturity, how far away it is from reaching black layer stage and being safe from the first killing frost. That table accompanies this article, so you can use it to help judge the maturity of your own fields.