Weather impact on Midwest corn 2011
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A break in the Midwest heat storm is a good thing, but is it good enough for the corn crop? A few days of temperatures exceeding 93 F – like we experienced in July – are “bad” for corn production, but consecutive days of the high temperatures are especially bad. When the heat comes as silking gets underway – as it did this year – the negative aspect is increased. Our mail indicates that ears did not pollinate well in at least major parts of fields across the Midwest and the locally grown sweet corn we have been consuming verifies that there are pollination problems this year. Many reported silking problems in late July. Shallow kernels, missing kernels, and tip back are common in field corn this year. All of this unfortunately sounds similar to what we experienced last year. As of Sunday, Aug. 7, 73 percent of Iowa’s corn was good to excellent condition, a significant change from 82 percent the week ending July 10 (USDA-NASS). The percent of Iowa’s corn silking and corn in or past the dough stage were slightly behind last year but slightly ahead of the 5-year normal. Some fields have reached the dent stage seemingly one to two weeks ahead of schedule. Remember though that kernels contain about 45 percent of their drymatter at dent and normally another month is necessary to complete the crop’s development. Fortunately the weather outlook for the next 10 days indicates that temperatures are likely to be on the low side of normal in the Corn Belt east of Des Moines, Iowa (Figure 1). The precipitation outlook shows a tendency toward normal for Iowa and neighboring states but less than normal rainfall for the areas further East, South, and West. 
Pollination and kernel set problems in northeast Iowa. Photo by Brian Lang, ISU Extension.
Corn development and temperature
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Figure 1. The outlook shows cooler than usual temperatures for Aug. 14-19 for northeast U.S. (also near the Pacific coast) and above normal temperatures are likely to the north and east of New Mexico.
Most areas in Iowa will have a reprieve from the heat during the next 10 days. However, the reprieve will not restore the loss of potential crop yield that was incurred by faulty pollination or by the accelerated pace of grain maturity. Areas south of I-80 will likely return to above normal temperature (Figure 2) during the week of Aug 16-22. Precipitation will be normal to dry from west to east across the Corn Belt.
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Figure 2. The 8 to 14 day outlook (August 18-22) indicates a likelihood of warmer than usual temperature across the Corn Belt to the south of I-80.
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