From Scientific American:

Incessant rains have turned Indiana farmer Larry Winger's grain fields into ponds, making it impossible for him to seed his corn crop.

"Historically, we would like the work to be done by the first of May, and research shows the optimal planting time is the last week of April," said Winger, who plants half of his 2,500 acres with corn, and the other half with soybeans.

"Prospects are OK until May 10, but after May 10, we start losing bushels," he added.

Delays in seeding pushed new-crop December corn futures at the Chicago Board of Trade about 7 percent higher in the past month, with prices climbing on fears that planting delays will reduce this year's crop at a time when corn stocks are at their tightest in 80 years.

For more, see: Soggy fields put U.S. farmers on a tight deadline