However, US farmers still expect to harvest nearly 79 million acres of corn and more than 72 million acres of soybeans in 2008, according to the latest acreage report.
The National Agricultural Statistics Service (NASS) collected the initial data for the annual acreage report during the first two weeks of June, before the majority of the flooding occurred in the Midwest.
But in an effort to more accurately determine how much of the planted area producers still intend to harvest for grain, it re-interviewed 1,150 farmers at the end of June in the flood-affected areas of Illinois, Indiana, Iowa, Minnesota, Missouri and Wisconsin.
Carol House, chair of NASS's Agricultural Statistics Board, said: "While many farmers are still assessing their damage and their options, this re-interview process provided a first look at how much of the planted corn and soybeans may remain standing for harvest.
"And what we are seeing is that the ratio of acres intended for harvest, compared to acres originally planted, is off about 2 percent from what we would have expected prior the floods."
The NASS acreage report shows US farmers planted 87.3 million acres of corn in 2008, down seven percent from last year's 93.6 million acres, but still the second largest area since 1946. Of that area, growers expect to harvest 78.9 million acres for grain. This is down nine percent from 2007 but still the second largest area since 1944.
For soybeans, 2008 planted area is estimated at 74.5 million acres, the third largest on record and up 17 percent from last year. Of the planted area, farmers expect to harvest 72.1 million acres, up 15 percent from last year.
In the Cedar Rapids area of Iowa, which is North America's top producing corn state, some companies were forced to close their plants due to flooding, including Cargill, Penford, Quaker and Swiss Valley Farms.
It was feared that the heavy rainfall could result in higher corn prices and at one point during the flooding, corn futures for July neared $8 per bushel.
However, by June 20, Iowa corn growers had already begun replanting crops as flood waters receded
The current price for July corn futures is $7.46 per bushel, according to the Chicago Board of Trade. The price for soybeans July futures hit highs above $16 last week and settled at $16.58.
For its August 12 crop production report, NASS is to supplement its standard survey activities by re-interviewing approximately 9,000 farmers in the flood-affected areas.
These re-interviews will be conducted in the middle of July, allowing time for flooded fields to dry and for farmers to fully assess their options. Additionally, NASS will increase the number of corn and soybean fields selected for objective field measurements.
Meanwhile USDA's Risk Management Agency is extending the deadline for submitting acreage reports for all 2008 crop year spring-seeded acreage in areas impacted by flooding and extreme weather conditions to August 15.
This additional time applies to spring-seeded crop acreage for all counties in Iowa, Illinois, Indiana, Kansas, Minnesota, Missouri, Nebraska, Ohio, South Dakota and Wisconsin.
The USDA weather report for the corn belt last week predicted that heavy showers would continue from Missouri to the eastern Great Lakes Region, causing additional flooding of low-lying farmland. But drier weather is bringing some relief from wetness to the upper Midwest.