To cause a massive food shortage in this country:

As the Des Moines and Raccoon rivers threatened to flood downtown in Iowa’s capital city, local and state officials cast the rising waters in epic terms, saying the next 24 hours could be one of the most important periods in the city’s 157-year history.

“This could be a 500-year type of event,” Iowa Gov. Chet Culver said, noting that three weeks of storms had left nine rivers in the state at or above record water levels, and had closed or washed out hundreds of roads, highways and bridges. “Very few people could anticipate or prepare for that type of event. … We’re dealing with something that’s historic in proportion.”

More than 2,800 people were evacuated Wednesday, including 1,800 in Cedar Rapids. Late in the day, there were signs the flooding that has killed 10 people could have an impact far beyond the upper Midwest. Forecasters watching the rising level of the Mississippi River were warning of potential flooding this weekend in St. Louis, about 350 miles downstream from Des Moines.

Meanwhile, the flooding is becoming an increasing threat to corn, wheat and other crops, raising the possibility that the storms here could contribute to already spiraling prices for food, fuel and other commodities. Besides ruining crops, the flooding has led the U.S. Army Corps of Engineers to plan on closing a 200-mile stretch of the Mississippi - the nation’s primary trade waterway - to agriculture and cargo ships.

[...] The turmoil in the nation’s breadbasket led the Agriculture Department this week to shave 3% from this year’s corn crop prediction, a rare move so early in the season. Corn topped $7 a bushel for the first time as heavy rains in Indiana, Illinois, Missouri, Iowa and Wisconsin � combined with growing demand for corn-based ethanol � pushed prices up.

“It’s clearly a panic situation,” said Gary Rhea, president of Risk Management Partners, a marketing firm here.

As much as one-quarter of the crops in the southern third of Wisconsin may be gone, said Paul Zimmerman of the Wisconsin Farm Bureau Federation. “We’re talking a couple hundred thousand acres of corn that could be in jeopardy” and a comparable amount of soybeans, he said.

Shipments of corn, grain and other farm commodities have been hit. The U.S. Army Corps of Engineers planned to close a 200-mile stretch of the upper Mississippi River between St. Louis and Rock Island, Ill., beginning today after rising water flooded locks and dams along the critical route for shipping grain and other cargo.

Ron Fournier, a Corps spokesman, said the section will be closed at least two weeks. He said any barges that don’t get through the locks Wednesday night are “going to get stuck wherever they are.”