Extreme heat has diverse impact on nation's corn crop

By Kris Bevill | July 20, 2011

It’s hot. Really hot. The recent “heat bubble” that has planted itself over the center of the U.S. has resulted in 13 deaths as of July 20 and prompted extended heat warnings and advisories across large parts of the nation that are more accustomed to dealing with Arctic-like temperatures than tropical weather. While the heat is a serious consideration for the human population, farmers and ethanol producers throughout the Midwest are keeping a wary eye on the weather for another reason - the corn crop.

Along the northern edge of the corn growing region in North Dakota, where July temperatures average in the mid-80s, heat indices have soared to around 115 degrees Fahrenheit for several consecutive days. Unlike the eastern Corn Belt, however, the crop there has not yet entered the critical silking phase so the heat has actually been beneficial for the corn, according to Joel Ransom, an extension agronomist with North Dakota State University’s extension service. “It’s the only good news we’ve had all year,” he said. Extremely wet conditions in the spring delayed planting by three weeks on average and continual rains have plagued the region all year. Therefore, the recent bout of heat has been welcome news for farmers there. “Anything that can get this crop moving along we want, and that’s what we’re seeing,” Ransom said. “We have a lot of water that needs to be moved out of our fields and the heat’s moving the crop and getting rid of some of that water.”

Economists at the University of Illinois said that unless the eastern Corn Belt receives a break from the extraordinary heat and recent dry spell, corn yields in that area will likely be down significantly this year. A yield comparison conducted by Darrel Good and Scott Irwin, members of the university’s agricultural and consumer economics department, shows that Illinois has a history of producing below average corn yields when hot, dry conditions are experienced in July. Unless conditions improve over the next few weeks, they predict a state average corn yield in the mid- to low-150s compared to a trend yield for 2011 of 168.7 bushels due to the fact that the recent heat wave hit just as most of Illinois’ corn is entering the reproductive phase of the crop, the worst possible time for excessive heat and little moisture. As of July 17, 62 percent of Illinois corn had entered the silking phase, according to Irwin. Up to 90 percent of the crop will be in the silking phase by the end of the month.

Irwin said Illinois needs cool, wet weather to finish off its growing season positively. Illinois’s corn harvest typically begins in mid-September, but prolonged dry weather and hot temperatures could bump up harvest by nearly a month, which would further reduce yields. “We still have 45 days of critical weather left so a lot can happen,” Irwin said. “If this persists, Illinois corn yields and yields throughout the eastern Corn Belt will be down sharply.”

While the heat has served as a much needed boost to the northern corn crop, Ransom isn’t quite ready to declare either victory or defeat. “Is it going to be enough? I don’t know,” he said. “We’re going to need some continued good weather (ideally 85 degree days and warm nights), but it’s giving us a boost. We’ll probably have less yield than last year, but it’s not a disaster everywhere. There’s some drowned areas that are worrying, but some of the stuff looks good too.”

The National Weather Service said most of the Midwest would again experience heat indices 100 degrees and higher on July 20, but a cold front pushing across eastern Montana is expected to soon provide some relief and a return to more typical summer temperatures.