The latest crop and weather report from the U.S.D.A. concludes the past week’s high temperatures and humidity were “good for the development” of most corn and soybean fields in Iowa, but farmers are concerned the “extreme” weather conditions in this critical month of August may damage the 2010 crop.

Jon Ostrander  has 1,500 acres of crops planted in north central Iowa, near Buffalo Center. “Crops look very good,” he says. “Both corn and beans.” But Ostrander has started seeing expanding dead zones in his soybean fields.

“We’re starting to get some sudden death in soybeans now, so there are starting to be some patches out there where it’s starting to die,” Ostrander says. “The plant just dies. It’s too wet, too humid, for too long.”

 This “sudden death syndrome” in soybean fields is a fungus disease moving across the Midwestern corn belt. Iowa State University Extension Field Agronomist Paul Kassel says it’ll cut yields. “It’s a root and stem rot. That’s been showing up in some large areas in central Iowa,” Kassel says.

“That’s going to hurt some fields, some locations quite a bit.” The U.S.D.A. still rates the Iowa soybean crop 73 percent good or excellent. The U.S.D.A. reports some Iowa farmers are seeing “yellow” stalks in their corn fields, as the plants haven’t gotten enough nitrogen.

However, 70% of the 2010 Iowa corn crop is rated good or excellent at this point in the growing season. Some of the largest corn harvests in Iowa history have occured in years when the temperatures in August have been cool. “I know we have advances in technology and that type of thing but, still, a corn plant likes it a little cool in August,” Kassel says. “so that’s a little bit of a concern.”

But while humans find these humid days of August tough, Kassel says the humidity helps the corn tolerate the heat.