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.
Iowa State University
Pope, Richard O., "Not a Bad Week, All in All" (2008). Integrated Crop Management News. 819.
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