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In ‘arms race against weeds,’ new weapons extend a losing strategy

More than 20 “superweeds” have the same herbicide immunities as genetically engineered crops.

Farmer Jake Conner stands in a field choked by Roundup resistant weeds.

Unless you are a regular reader of Chemical & Engineering News, you might have missed this battlefield report yesterday from American agriculture’s ongoing war against natural selection:

Farmers, plant geneticists, chemists, and agronomists recently have been engaged in an arms race against weeds, particularly weeds that have evolved resistance to the common herbicide glyphosate.

A second generation of herbicide-tolerant crops has been developed to battle resistant weeds, but they have sparked concerns about overreliance on chemical controls.

I guess it was the phrase “arms race against weeds” that got my attention, for C&EN typically is not in the camp of skeptics regarding the technological promise of, say, chemistry or engineering.

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And while this article quotes a few dissenters for balance, its overall tone ranges from favorable to fascinated regarding the new products being rolled out by Monsanto, Dow AgroScience and others.

Still, I cannot think of a better metaphor than “arms race” — with its connotations of vast expense and fundamental futility — to describe American agriculture’s misadventure with these products over the last 15 years.

In the beginning, Roundup

Glyphosate, of course, is the best-selling herbicide in America, introduced as Roundup by Monsanto in the 1970s. A remarkably effective and comparatively benign herbicide, it killed more kinds of weeds than its competitors, was less threatening to human and animal health, and broke down more quickly into harmless components.

(I’ve personally found it a miraculous product for taking out every noxious plant I’ve ever treated, including buckthorn trees; also an unfortunate few I didn’t mean to treat, thanks to spray drift.)

Because it must be applied to growing plants, Roundup wasn’t much use in production agriculture, which prefers pre-emergent soil treatments — until 1996.

That’s when Monsanto introduced “Roundup Ready” soybeans, genetically engineered to tolerate broadcast spraying of glyphosate over huge farm fields. Since then the market has welcomed tolerant varieties of corn, canola, cotton, sorghum, alfalfa, sugar beets and, I read the other day, Kentucky bluegrass.

Everybody knew that natural selection would respond with Roundup-resistant “superweeds”; the only question was how long that might take, and how far they might spread – like drifting herbicide spray – beyond the agricultural zones.

But in the short run the Roundup-tolerant crops returned big cost savings – and perhaps even bigger environmental benefits – by displacing nastier herbicides and by reducing mechanical tilling for weed control, which promotes soil erosion and chemical runoff.

Within five years of introduction, glyphosate-tolerant soybeans accounted for almost 7 of every 10 acres planted across the United States; today the figure is 94 percent, according to the U.S. Department of Agriculture. For corn, the figure is 72 percent, and for cotton it’s 73 percent. Minnesota was above the national averages last year at 95 percent for soybeans and 77 percent for corn.

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And now we are in the long run.

At least 20 ‘superweeds’

Various studies of glyphosate-resistant weeds put their number at 20 or more. Some suggest the first to be detected was a form of ryegrass found in Australia in 1998, in an orchard where weeds had been treated with glyphosate for a relatively short 15 years.

In the United States, resistant varieties of pigweed, horseweed and giant ragweed are among the principal threats. In Canada, the special nuisance is a form of fleabane, and earlier this month the Ottawa Citizen took a long look at the struggle to contain the new  pests —including hand-weeding at $100 an acre.

Dow AgroScience, a principal Monsanto competitor, helpfully provided C&EN with a chart showing the state-by-state prevalence of glyphosate-resistant weeds across roughly half the land area of the lower 48 states. Minnesota was in the mid-range with three species; further south, some states had five or six; Mississippi led the pack with seven.

If you recall Monsanto’s assurances that the genes conveying glyphosate resistance would never escape the engineered plants and show up in weed species, you recall correctly. And, as you might expect, the herbicide companies’ answer to the genie’s escape from the bottle is more herbicide, more combinations of herbicide, and more varieties of herbicide-tolerant crops.

Dow is seeking USDA approval for corn engineered to be tolerant of 2,4-D, a widely used weedkiller that predates glyphosate (it was a key component of the Agent Orange); it hopes to start marketing the new variety next year. Monsanto hopes to follow in 2014 with soybeans resistant to the herbicide dicamba.

Sygenta and Bayer CropScience are among the other companies at work on engineering new crop varieties, and considerable work is going into developing plants with “stacked” tolerance of multiple herbicides.

All seem to be urging farmers to consider rotating their herbicide applications instead of using the same chemical year after year after year – but not to consider whether herbicide reliance itself is eventually doomed to fail because Mother Nature, after all, bats last. According to C&EN:

For their part, Dow and Monsanto insist that the lessons learned from overreliance on glyphosate are changing farming practices. Never again, they say, will it be the norm to use the same herbicide, year after year, on the same crop in the same location. They dispute estimates that the use of 2,4-D or dicamba will greatly increase. And both firms have developed new, low-drift formulations of these herbicides that they say will minimize off-field migration….

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Crops that contain the 2,4-D tolerance trait will also tolerate older versions of 2,4-D. However, Dow has developed a stewardship program that obligates farmers to use a premixed combination of 2,4-D choline and glyphosate. The program includes farmer education about using multiple herbicide modes of action, the requirement to use Dow’s new herbicide mixture, and labeling instructions for proper application….

More herbicide-resistant traits are in the pipeline, which will increase the availability of diverse modes of action. For example, Syngenta and Bayer CropScience are collaborating on a p-hydroxyphenylpyruvate dioxygenase herbicide-tolerance trait for soybeans. And crops tolerant of three or more herbicides are not far behind.

What of the other lesson – that new products and practices inevitably beget new “superweed” pests, and that it therefore may be time to consider going back to tilling and other mechanical practices of weed control?

Unfortunately, it’s possible that farmers themselves have evolved in response to these new agricultural practices, and not in a beneficial way.

David R. Shaw, a Mississippi State professor who heads a weed-resistance task force for the Council for Agricultural Science & Technology, told C&EN that

Roundup Ready was so good, farmers could forget what they knew in terms of weed management. Before that, there were no silver bullets. There is now a whole generation of farmers that haven’t known anything but this very simplistic system.