Waterhemp continues to get more difficult to manage as scientists this year confirmed the first case of waterhemp with six-way resistance, according to the Weed Science Society of America (WSSA).

A waterhemp population in northern Missouri was treated with eight herbicides, and scientists found 16 percent of the plants in the studied weed population contained genes stacked for six-way herbicide resistance — 2,4-D, atrazine, chlorimuron (ALS inhibitor), fomesafen (PPO inhibitor), glyphosate and mesotrione (HPPD inhibitor). Only dicamba and glufosinate provided accepted control.

In Iowa, waterhemp has demonstrated resistance to five different groups of herbicides, said Bob Hartzler,...