By Rich Pope, Department of Plant Pathology
The week ending July 13 was close to average in terms of temperature, and crops have generally made slow but steady improvement in condition over the period.
Normal daily accumulations of degree days vary throughout the year, with July obviously being warmer than May. An average Iowa mid-July day produces about 24 base-50 degree days in the northern third, around 25 in central counties and 26 to 27 in the southern third of the state. That means that currently, we are about four to five full developmental days behind average for the season from May 1 through July 13. Of course, a late-planted field missed the heat gained while it was in the bag, and is that much more behind in development.
Once crops shift to reproductive (the “R” stages for corn and soybean), the temperature game changes slightly. Corn development from silking through maturity is promoted by warm days (upper eighties and low nineties) with adequate moisture. Relatively cool nights during grain fill are also good for the crop, with cool meaning temperatures in the lower 60s. Cooler nights keep the corn living a few days longer to gain more dry matter.
Rich Pope is an extension specialist with the Corn and Soybean Initiative.
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