A study featured in the journal Weed Science is certain to keep many corn and soybean growers up at night. Researchers have identified a waterhemp population in Missouri that is resistant to a record-breaking six herbicide mechanisms of action.

It all started when growers in Randolph County, Missouri, reported a population of waterhemp that appeared to be resistant to 2,4-D. Researchers from the University of Missouri conducted field experiments that confirmed the 2,4-D resistance. But they also found the same waterhemp population was resistant to atrazine, chlorimuron, fomesafen, glyphosate and mesotrione. Of the eight herbicides applied, only dicamba and glufosinate provided acceptable control.

Listen: Rural Radio Network interview with University of Missouri researcher Lovreet Shergill

The results are sobering – especially for anyone waiting on the approval of 2,4-D–resistant corn and soybean as a way to manage glyphosate resistance. If we’re already seeing 2,4-D resistance now, what will happen when use of the herbicide becomes even more commonplace?

Researchers say six-way resistant waterhemp demands a diversified approach. Rather than relying on glyphosate, 2,4-D or any other single herbicide, it’s time to focus on a variety of appropriate cultural, mechanical and biological control tactics.

Read the full text of the article “Investigations of 2,4-D and Multiple Herbicide Resistance in a Missouri Waterhemp (Amaranthus rudis) Population” in Weed Science Vol. 66, Issue 3.