An Iowa State University demonstration plot north of Ames highlights the perils of relying on a single herbicide site of action for weed control.

Waterhemp blew through various standalone herbicide treatments in the plot, which has a history of herbicide resistance after more than a decade in seed corn production, said Meaghan Anderson, ISU Extension field ag­­ronomist in central Iowa.

“We know seed corn has a history of herbicide resistance, particularly with HPPD herbicides,” she...