While Palmer amaranth grabs the headlines, common waterhemp continues to be the biggest headache for Iowa farmers.

"Common waterhemp is one of the hardest weeds to control in Iowa and probably our biggest weed concern," says Angie Rieck-Hinz, Iowa State University (ISU) Extension field agronomist in north-central Iowa.

Still, Palmer is a growing concern in Iowa. ISU recently alerted farmers to be on the lookout for the weed, which has been devastating to farmers in southern states. By mid-August, Palmer had been reported in a dozen Iowa counties.

Palmer amaranth and waterhemp have a close resemblance to each other. "Because of waterhemp’s omnipresence in fields across Iowa and the...