As weeds are missing the last weeders, farmers are running out of options

About 20 years ago, farmers thought that they would finally have conquered weeds forever.

Biotech companies have given them a new weapon: genetically modified crops capable of tolerating doses of the herbicide glyphosate, also known by its trade name, Roundup. Farmers could spray this chemical directly on their crops, weed control and crops were doing well.

Stanley Culpepper remembers that moment. He had left his family's farm to study weed science at North Carolina State University. "I've been trained by really great people," he says, "and I've even learned that there's never a weed that's so resistant to Roundup."

These scientists thought that the plants could not be immunized against Roundup because it required a too important change in the biology of the plant.

However, in 2005, Stanley Culpepper claimed to have discovered weeds that Roundup could not kill. They grew up in a field in Georgia. And it was not any weed. It was a kind of monster called Palmer amaranth, or amaranth.

In subsequent years, these glyphosate-resistant amarons spread like a sore on US farmland. They are virtually everywhere in the South now and are becoming more common in the Midwest.

"The impact is incredible," Culpepper said. "We have invested more than $ 1.2 billion, just in the cotton industry, to fight against glyphosate resistant amaranth Palmer since its discovery."

Biotech companies have therefore launched a new solution: new varieties of genetically modified soybeans and cotton that can tolerate two other herbicides, called dicamba and 2,4-D. Farmers can plant these crops and then spray these chemicals, often in addition to glyphosate, to destroy their weeds.

Many new products are offered to farmers and pesticide manufacturers. In particular, dicamba-tolerant crops have been controversial. But now, even before they are fully launched, there is evidence that this weed control tactic could begin to fail.

The evidence is in a greenhouse at Kansas State University, carefully maintained by Chandrima Shyam, a graduate student.

"These are plants that have been sprayed with 2,4-D, and they are resistant plants," she says. "You can see that resistant plants are quite vigorous."

I see trays and trays of amaranth flowering. They are the offspring of the weeds that another Kansas scientist, Dallas Peterson, noticed last summer in a field where he conducts research. They seemed to survive all the chemicals that he was throwing at them.

"We simply were not able to control or eliminate these weeds after these herbicide applications," he said.

He enlisted a colleague specializing in herbicide resistance research, Mithila Jugulam, who in turn asked Shyam for help.

"So we went to the field, we dug whole plants, we took them to the greenhouse and isolated them," says Shyam.

They cultivated 10 Palmer amaranth seedlings until they produced seeds and then replanted them to produce new generations of plants to study them. They discovered that these amaranths can survive 2,4-D sprays. Some plants also appear to be immune to dicamba, although this remains to be confirmed. The plants are probably also resistant to glyphosate.

Basically, they are a farmer's nightmare. And if they present themselves in one area, they are probably also in others.

Stanley Culpepper, of the University of Georgia, says he's not surprised. No one should be surprised by the super powers of amaranth, he says. "As a weed scientist, I tell you, it's just an absolutely fascinating plant," he said. "You must respect it, and the first thing to respect is, [know that] this factory will surpbad me if I do the same thing over and over again. "

Culpepper tells farmers that they can still control this supergrbad, but they have to use a lot of different tools. This means that you have to deploy multiple chemicals, alternate the crops that they plant and plant extra "cover crops" out of season to cover the soil and make it more difficult to weed weeds.

Matt Coley, a farmer from Vienna, Georgia, says that most growers have learned a lot from their experience by losing Roundup as a miracle solution to weeds. "As long as we continue to follow the recommendations of not relying solely on a chemical, I think we can continue to manage cabbage amaranth," he says.

However, dicamba and 2,4-D are among the herbicides he uses for his cotton crop, and he admits it's a bit disturbing to hear about Palmer's amaranth plants as these chemicals will not kill. He hopes to have new weapons in his arsenal. "The industry, the manufacturers – for which they are in business, they must have farmers," he says. "I hope they use their research and development to continue to provide us with products that will help us control our pests in our crops."

The arsenal is exhausting, though. And that is what worries most Culpepper. "We have not had a new way of destroying a weed with a herbicide since 1984," he says.

Meanwhile, weeds such as amaranth Palmer and ryegrbad have destroyed one chemical after another. "It's a monumental challenge we face." Amaranth with dicamba and 2,4-D resistant is surprisingly "No," he says. "[But] the general problem of resistance is downright overwhelming. "

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