In southern Wisconsin, where irrigation is less prevalent, farmers worried recent rains would have little effect on a crop that struggled through the driest planting season in decades.

And in Indiana, where sizzling weather has devastated large swaths of farmland and shortened the pollination cycle to only a few days, farmers fear strong winds from the remnants of Hurricane Isaac could flatten their already hard-hit fields.

"As you walk through the fields, you have to be careful because if you touch a stalk too hard, it will fall over," said Johnson, who farms 1,200 acres of popcorn at his family's farm in Jay County, in eastern Indiana. "We get anything 30 mile an hour, we'll lose what crop we have."