A leading Iowa ag entrepreneur wants the U.S. government to block pending mega-mergers among leading seed and chemical companies, saying the deals pose a serious threat to farmers.

Bruce Rastetter, CEO and founder of Iowa-based Summit Agricultural Group, says proposed mergers such as those between Dow-DuPont, Bayer-Monsanto and Syngenta-ChemChina will limit competition, stifle innovative research and stunt job growth, eventually leading to increased costs for farmers.

“Mergers like this have the potential to put into motion irreversible damage to agriculture,” said Rastetter, who also serves as president of the Iowa Board of Regents. “With fewer ...