U.S. grain elevators on the Gulf coast are shut and barges carrying grain on the lower Mississippi River halted in preparation for Hurricane Isaac.  Isaac, which has been rolling over the Gulf of Mexico toward Louisiana, strengthened Tuesday into to Category 1 hurricane with 75 mph winds. The storm is on track to slam into New Orleans, with hurricane warnings extending  across 280 miles from Morgan City, Louisianna., to the Florida-Alabama state line. , which s due to make landfall late Tuesday or early Wednesday, Reuters reports.

Archer Daniels Midland closed four grain export elevators in New Orleans, while Cargill said elevators in Westwego and Reserve, Louisiana, will be closed. Bunge Ltd is shutting down an export facility in Destrehan, Louisiana because of a mandatory evacuation order in the area, Reuters reports.

The Mississippi River is a major shipping channel for grain produced in the Midwest farm belt to export terminals at the Gulf of Mexico, where it is then shipped worldwide. Midwest farmers, who produce 75 percent of the country's corn and soybeans are due to begin harvesting in the next few weeks.