Corn prices plunged last week after the U.S. Department of Agriculture (USDA) estimated corn plantings and yields well above the expectations of farmers and crop market analysts despite a record number of prevented planting acres.

Uncertainty regarding the size of this year’s crops is likely to linger into harvest due to delayed planting and development, said Sam Funk, Iowa Farm Bureau Federation chief economist.

"I think there’s still a downward bias on what total production could be," he said. "We’re testing the ability of modern seed to produce under challenging conditions."

In its August crop production report, which included a resurvey of acreage in 14 states due to delayed planting, the USDA...