Corn yields continue to astonish many Iowa farmers as they push toward the end of a long harvest season.

“In general, corn is 30 to 40 bushels better than expected. Some areas are even better than last year,” said Jim McDermott, a DEKALB Asgrow technical agronomist in northwest Iowa. “The thing that we didn’t expect to see was this top end in corn. In some cases, guys are seeing 240 to 270 bushel yields.”

Corn...