Missouri scientists find waterhemp resistant to 6 herbicide modes of action

waterhemp
Waterhemp — photo courtesy University of Missouri

A group of scientists recently reported a population of waterhemp in Missouri resistant to a record-breaking six herbicide modes of action.

Their findings were recently published in the Weed Science Society of America’s journal, Weed Science. The authors included Lovreet Shergill, Blake Barlow, Mandy Bish and Kevin Bradley, all with the University of Missouri’s Weed Science Department.

It all started when growers in Randolph County, Missouri, reported a population of waterhemp that appeared to be resistant to 2,4-D.

University of Missouri researchers conducted field experiments that confirmed 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, according to a WSSA news release.

The results are sobering – especially for anyone waiting on the approval of 2,4-D–resistant corn and soybeans 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.

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