Sunday’s Des Moines Register carried the latest journalistic exploration of herbicide-resistant “superweeds” on Iowa farmland. The story’s not new: agronomists at Iowa State University anticipated this problem and have been warning farmers for at least 15 years. Various published studies have shown the connection between widespread corn and soybean farming practices and the “rapid selection of 21 species of glyphosate-resistant weeds.”
Industry groups representing conventional growers have repeatedly accused advocates for clean water and sustainable farming of threatening rural Iowans’ way of life. Yet the dominant practices of corn and soybeans growers have accelerated the spread of resistant weeds through natural selection, potentially putting many Iowa farmers out of business in the coming years.
After the jump I’ve posted excerpts from Donelle Eller’s story for the Sunday Register and more background on the herbicide-resistant weed problem. The 2013 Union of Concerned Scientists briefing paper on “The Rise of Superweeds-and What to Do About It” is an excellent starting point.
Why resistant weeds are spreading is no scientific mystery. Iowa State University agronomist Michael Owen has described the trend as “natural selection on a fast track.”
“There is nothing ‘super’ about them [superweeds]. They don’t grow any faster, get any bigger or produce more seeds than non-herbicide-resistant weeds of the same species,” Owen said.
Nor, Owen said, are they harder to kill when treated with an effective method.
The trouble is, the method many farmers thought was foolproof – spraying glyphosate on fields planted with seeds that are genetically engineered to tolerate the chemical – has accelerated the evolution of weeds that are increasingly resistant to the most popular weed killer in America, the broad-spectrum, systemic herbicide commonly known by the Monsanto brand Roundup. […]
In Iowa, waterhemp, giant ragweed and horse weed (also known as marestail) have documented glyphosate resistance. Several other weeds are suspected to have developed resistance.
It was predictable, said Owen, who predicted it in the late 1990s, not long after Monsanto introduced the first seeds genetically engineered to withstand Roundup. […]
The herbicide kills susceptible weeds, leaving only those with resistance traits to pass their genes to the next generation. With a new generation produced each year, it’s evolution in hyperdrive.
Crop acreage with weeds resistant to the most common herbicide, glyphosate, the active ingredient in Monsanto brand Roundup, has doubled from 32.6 million in 2010 to 61.2 million in 2012, according to a report by Stratus Agri-Marketing, which conducts annual glyphosate resistance tracking studies.
The Union of Concerned Scientists explained the problem this way in its briefing paper on “The Rise of Superweeds.”
In the 1990s, Monsanto introduced a new line of seeds called “Roundup Ready,” which were genetically engineered to be immune to glyphosate, the active ingredient in the company’s patented herbicide, Roundup.
Roundup Ready seeds were expensive, but they were widely adopted because they made weed control easier. And because glyphosate is less toxic than other common herbicides, the Roundup Ready system was hailed as an environmental breakthrough.
But there was a catch: as more and more farmers used more and more Roundup, genes for glyphosate resistance began to spread in weed populations. The growth of resistance was accelerated by a trio of factors:
Monoculture. Growing the same crop on the same land year after year helps weeds to flourish.
Overreliance on a single herbicide. When farmers use Roundup exclusively, resistance develops more quickly.
Neglect of other weed control measures. The convenience of the Roundup Ready system encouraged farmers to abandon a range of practices that had been part of their weed control strategy.
Estimates of actual herbicide use on U.S. soybeans through 2007, as well as future rates forecast by weed scientists. Adapted by permission from Mortensen et al. 2012. (Click for larger version.)
This “perfect storm” of accelerating factors has quickly turned the Roundup resistance problem into a superweed crisis. And because many farmers can no longer rely on glyphosate alone, overall herbicide use in the United States-which Roundup was supposed to help reduce-has instead gone up (see graph at right).
Sustainable agriculture advocates have promoted alternative growing methods, crop rotations, and diversification for years, but federal policy still encourages Iowa farmers to stick with the standard corn/soybeans rotation. In addition, corporations selling seed, chemicals, or farm equipment have tailored their products to that model.
Eller’s feature for the Des Moines Register focused on Palmer amaranth, a plant one farm writer described as a “pigweed-on-steroids.” From the Sunday Des Moines Register’s June 22 edition:
Even a moderate infestation of Palmer amaranth can rob farmers of about two-thirds of their corn and soybean yields, experts say.
That would be about $11 billion gone from last year’s total $16 billion corn and soybean receipts. That money ripples through some of the state’s most important agricultural businesses, a lineup that includes DuPont Pioneer, Sukup Manufacturing Co. and Deere & Co. Economists estimate that a quarter of Iowa’s $166 billion gross domestic product is tied to farming.
The growth of herbicide resistance means farmers will use more – and potentially more toxic – chemicals to battle the aggressive weed.
Agribusinesses are introducing a new lineup of herbicides and seeds to the battle. Environmental groups worry that those proposed solutions will only worsen the problem.
“Increased herbicide use on the new engineered crops will speed up weed resistance, leaving no viable herbicide alternatives,” said Doug Gurian-Sherman, a senior scientist with the Union of Concerned Scientists. “This is a dangerous chemical cocktail that, when combined with the current farming system, it’s a recipe for disaster.” […]
“Even though we warned them, you understand the economics behind it,” said Robert Hartzler, an ISU professor of agronomy. “The current system favors the growth of corn and soybeans,” prompting farmers to leave out rotations of other crops such as winter wheat that could disrupt weed resistance.
“To make a reasonable living, you need to farm large acres, and to farm large acres, you need to cover acres quickly and that involves herbicides. Glyphosate was the best herbicide around,” Hartzler said.
“You couldn’t sit down at a blackboard and come up with a better rotation than we have for weeds to thrive in,” he said.[…]
“If we use one single system, one tool to control a pest, Mother Nature will find a way around that tool,” said Brent Wilson, DuPont Pioneer technical services manager. “That’s just the law of nature.
“It’s too bad that glyphosate is developing resistance, but it shouldn’t surprise us,” Wilson said. “We don’t know of any herbicide that won’t develop resistance over some time.”
P.S.- The same factors that have promoted the growth of “superweeds” have accelerated the evolution of pests resistant to genetically modified crops.