Things could be worse. Much Worse. The midwest has been suffering thru a drought this summer and corn yields will be below normal. This will result in fewer barges needed.
Even with the Gulf Terminals open for business in good times, occasionally it is necessary, for grain elevators in little country towns, to store grain on the ground once all their bins are full.
Agriculture will adapt.
Of far greater concern is the shortage to diesel fuel necessary to harvest the crop.
For all intents and purposes, the port of New Orleans has been shut down for almost two weeks, with navigation being allowed in the past few days. The majority of the export elevators are in St. Charles Parish northward, which has not been affected with the flooding that occurred in Jefferson, Orleans, St. Bernard and St. Tammany parishes.
What is actually occurring from the midwest farmer's viewpoint is that the availability of barges to load has decreased dramatically (barges waiting to unload in New Orleans now), which is making what few that are available much more costly. For example (supply and demand), what may normally cost $9 per ton to ship in the normal harvest season is projected to cost $27 per ton. This will cause farmers to hold product until they have a better margin of return (which is normal). The only ones paying the penalty will be those that require selling to fund operations.
One of the main drawbacks in getting things back to normal in New Orleans deals with the available work force. Power and utilities can be restored, but if your workers are no longer in the area you won't be able to operate.