Many farmers, including Mueller, look to store much of their new crop until December or January, when they could get a better price. Without room at grain elevators, they'll have to find bin space on their farms or do what growers dread: Store the corn on the ground and risk seeing it rot, as was the case last year at many elevators that struggled to handle the record crop.

Farmers could opt to hold off on their harvests — a prospect carrying its own risk of subjecting the crops to devaluing added moisture as autumn approaches. Bringing in the crops now could save on drying costs, letting nature do the job instead of pricey propane.

"That's the box a lot of folks are in," said Leon Corzine, the National Corn Growers Association's president who grows corn on 2,000 acres near the central Illinois town of Assumption.

Protracted river traffic jams at New Orleans could force shippers to rely on rail or trucks — more expensive options, notably with fuel costs soaring. Midwest grain instead could be routed to the Pacific Northwest for shipping overseas, assuming farmers can find the rail cars and trucks already in tight supply to get the grain to those ports.

The problems confirm pre-Katrina concerns raised by University of Nebraska agricultural economist Dennis Conley that even a moderate disruption of exports at New Orleans could cost up to $900 million in lost corn exports.

"This is of a scale that will be felt for a long time," Conley says, "for months and probably into next year."