Weed resistance – Palmer amaranth marches north

Three years ago, Dr. Ford Baldwin stood in a field near Widener, Arkansas, and spoke of the many challenges facing growers in the Mid-South of the U.S. He talked about the advance of resistant weed species and how, five years prior to that, he’d written about the looming “train wreck” represented by glyphosate resistance. He made his presentation standing in front of a soybean field that had been overrun with glyphosate-resistant Palmer amaranth. When he began writing about the wave of weed resistance that was coming because of over-reliance on glyphosate, few heeded his advice.

Since that presentation in 2010, several things have happened — Palmer amaranth has migrated northward with astounding speed, progressing quickly through Missouri and into Illinois and Indiana, to the point where it is now in Michigan. And the problem with its rapid advance is that it must be treated as though it’s resistant to glyphosate, because it likely is. The other change is that Baldwin says he no longer makes similar presentations in the Mid-South region of the U.S. because farmers either don’t listen to what he says, or the problem with resistance has become too overwhelming to be of much help.

Baldwin, a weed specialist with Practical Weed Consultants of Austin, Arkansas, was part of Bayer CropScience’s “Dead Weeds Tour,” held at the company’s research station, Thursday, July 18, near Rockwood, Ontario, northeast of Guelph. He provided a brief history of weed management tools, relating how atrazine gave way to Group 2s, followed by the seemingly miraculous arrival of glyphosate.

Baldwin says times have changed dramatically. The resistance issue has changed farming’s landscape through Arkansas, to the point where farmers are going through foreclosure and land isn’t being rented, mostly because farm renters don’t want poor, hard-to-control, weedy land.

“(The resistance issue) has changed everything for us,” said Baldwin, adding that some farmers have reached the extreme where they’ve been forced to hand-weed their fields. “We’re doing more tillage than we wanted to, and this year, everything’s backwards again. Farmers just got complacent with Roundup Ready technology.”

In 2010, the field tour in Widener was to promote the benefits of the LibertyLink technology, together with the launch of Ignite (glufosinate), a formulation that Baldwin referred to as a “diversity tool.” The challenge however, is an old one; many farmers still believe that there’s a “new glyphosate” waiting to be developed, and Baldwin spoke of how farmers in the Mid-South overused glufosinate, something which he had predicted, and advice that went “right over the heads of most.”

He also mentioned that the LibertyLink system is in the process of being joined by dicamba-resistant, 2,4-D-resistant and HPPD technologies, which will inevitably be incorporated as stacked-trait technology.

“But after that, that’s it — we’re using up our technologies, one at a time,” said Baldwin, referring to the manner in which U.S. farmers are — again — overusing the latest technologies. Waterhemp, he noted, is now resistant to five different modes of action in various states of the Midwest and the Plains (glyphosate, ALS-inhibitors, HPPDs, 2,4-D and the triazines).

It’s one reason why he speaks at Canadian events such as this, to share the same message that’s widely been ignored in the U.S., and hope for a different response.

“So you’re either going to follow us off the cliff or find a different direction,” said Baldwin. “When you do the same thing over and over, bad things are going to happen. What you need is to get smarter than a weed that doesn’t have a brain!”

He then cited the approach taken by an Iowa farmer, who was a co-speaker with Baldwin at an event in the Midwest. This particular farmer rotates his technologies — Roundup Ready with LibertyLink, as well as his herbicides, including atrazine and HPPDs on his corn. And although he doesn’t have resistant weeds on his farm, he manages his fields as though he does, even hand-weeding his escapes.

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