Thirsty Corn In Iowa and Illinois

Reuters: 

Iowa and Illinois - which produce about a third of all U.S. corn and soybeans -- are threatened by the harshest heat wave in more than half a century. Blistering temperatures, combined with little rain, are stressing corn during pollination, the key growth stage.
"By Sunday or Monday if we don't get rain here we will be losing anywhere between 7 to 9 percent of our yield potential," said Roger Elmore, corn agronomist at Iowa State University in Ames, Iowa. "If it drags on into next week, it is going to be worse."
Drought conditions, which intensified during the past week across the central United States, have caused irrevocable damage to crops in Missouri, Indiana and even southern Illinois, where farmers are cutting stunted corn for silage, a low-grade feed for cattle.
"Next week is critical for Iowa," said Elmore. "Even the crops on good soils are going to start showing a lot of stress going into next week if we don't have rains soon."
Mike Hutjens, University of Illinois professor of animal sciences, said corn plants, especially in the southern third of the state, are showing irremediable stress from the heat and drought.
"Corn plants are firing from the roots up the stalk of the corn plant," he said, meaning stalks are drying out. "Some corn has tasseled, which may not pollinate, resulting in barren corn stalks" with no ears of corn.

We are well beyond the 7 to 9% yield hit mentioned here.  Based on what the corn looks like, and the weather forecast, I'd say we're at the 30 to 50% yield hit point.  That may be overly pessimistic, but that is what my gut tells me.