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Travis Legleiter, Purdue University
WHEATFIELD, Ind. — The Terminator — that relentless, seemingly indestructible villain of the 1980s action movie — is back. And he is living amid the soybeans at Harper Brothers Farms.
About 100 miles northwest of Indianapolis, amid 8,000 lush acres farmed by Dave Harper, his brother Mike and their sons, the Arnold Schwarzenegger of weeds refuses to die. Three growing seasons after surfacing in a single field, it is a daily presence in a quarter of the Harper spread and has a foothold in a third more. Its oval leaves and spindly seed heads blanket roadsides and jut above orderly soybean rows like skyscrapers poking through cloud banks. It shrugs off extreme drought and heat. At up to six inches in diameter, its stalk is thick enough to damage farm equipment.
“You swear that you killed it,” said Scott Harper, Dave Harper’s son and the farm’s 28-year-old resident weed expert. “And then it gets a little green on it, and it comes right back.”
Botanists call the weed palmer amaranth. But perhaps the most fitting, if less known, name is carelessweed. In barely a decade, it has devastated Southern cotton farms and is poised to wreak havoc in the Midwest — all because farmers got careless.
Palmer, as farmers nicknamed it, is the most notorious of a growing number of weeds that are immune to the gold standard of herbicides, glyphosate. Cheap, comparatively safe and deadly to many weeds, glyphosate has been a favorite ever since the Monsanto Company introduced it under the name Roundup in the mid-1970s.
After Monsanto began selling crops genetically engineered to resist glyphosate in the 1990s, the herbicide’s use soared. Farmers who once juggled an array of herbicides — what killed weeds in a cotton field might kill cornstalks in a cornfield — suddenly had a single herbicide that could be applied to almost all major crops without harming them.
There were even environmental benefits: Farmers relied less on other, more dangerous weed killers. And they abandoned techniques like tilling that discouraged weed growth, but hastened erosion and moisture loss.
But constantly dousing crops in glyphosate exacted a price. Weeds with glyphosate-resisting genetic mutations appeared faster and more often — 16 types of weed so far in the United States. A 2012 survey concluded that glyphosate-resistant weeds had infested enough acreage of American farmland to cover a plot nearly as big as Oregon, and that the total infestation had grown 51 percent in one year. Glyphosate-resistant palmers first surfaced in 2005, in a field in Macon County, Ga. Nine years later, they are in at least 24 states.
“There’s no substantive argument about whether the problem’s gotten far worse in this era of genetically resistant crops,” said Charles Benbrook, a professor and pesticide expert at Washington State University.
“The advent of herbicide-tolerant crops made it possible for farmers to load up so much herbicide on one crop that it was inevitable that it would develop resistance.”
Now farmers are going back to older techniques to control weeds, using more varieties of herbicides, resuming tilling — and worse.
Palmer amaranth is the prime example. Consider the cotton fields that blanket many Southern farms: Without glyphosate, almost no herbicides can kill the weed without also damaging cotton plants. Some farmers have mowed their crops to keep palmer seeds from maturing. In 2009, Georgia spent $11 million to send laborers into a million acres of cotton fields to pull palmers out by hand.
For many farmers, including the Harpers, manual labor has become a last resort in the battle against carelessweed.
“I consider myself a Roundup baby, and it was great,” Scott Harper said. “You didn’t have to think about anything. And now we get this weed that flips everything on its head.”
The Harpers’ 2,500-acre soybean crop is an object lesson in palmer’s adaptability and how far farmers must go just to keep it in check.
Palmer amaranths seem as if they were designed by nature to outwit herbicides and farmers. Unlike many weeds, it has male and female versions, increasing genetic diversity — and the chances of a herbicide-resistant mutation — in each new seed. And each plant is astonishingly prolific, producing up to 200,000 seeds in an average field, said Dave Mortensen, a professor of weed and plant ecology at Pennsylvania State University.
“If one out of millions or billions of seeds contains a unique trait that confers resistance to herbicide,” he said, “it doesn’t take long when a plant is that fecund for it to become the dominant gene.”
William G. Johnson, a Purdue University professor of botany and plant pathology, said the weed probably arrived at the Harpers’ farm in typical fashion: in manure, purchased as fertilizer, from cows that ate cottonseed — and, inadvertently, palmer seeds.
The Harpers initially mistook the weed for waterhemp, a close relative. Before they learned otherwise, combines had already harvested fields containing mature palmer seed pods and had spread the seed far and wide.
A glyphosate-resistant palmer is a mighty beast indeed. Its seeds can germinate any time during the growing season, so herbicide sprayed in April is useless against a palmer that appears in July. Once sprouted, palmer amaranth can grow more than two inches a day. Once it exceeds four inches, even herbicides for which it lacks resistance begin to lose their effectiveness.
The Harpers have kept palmers at bay in their 5,500 acres of corn by spraying dicamba, a weed killer that is benign to corn. Soybeans are a different matter.
Last year, the Harpers sprayed palmer-infested fields several times with glyphosate and two other herbicides, pushing herbicide costs to $80 an acre from $15. About eight in 10 palmers died. The rest wilted for a couple of weeks, then resumed growing.
This year, they are trying a different chemical cocktail that raises herbicide costs only to $45 an acre. Their big gun, a herbicide that blocks palmers from synthesizing amino acids, was sprayed on July 3, the first of two applications allowed each summer.
“I came back from the Fourth of July weekend, and they looked dead,” Mr. Harper said. “I said, ‘I think we smoked ’em.’ My dad says, ‘Awesome.’ ” He paused. “Ten days later, there’s green coming all over them again.”
Should the second herbicide application fail, Mr. Harper said, he is unsure what to do next.
More broadly, experts in glyphosate’s travails — farmers, scientists, regulators, the herbicide industry, environmentalists — feel much the same way.
The industry has readied a new barrage of genetically engineered crops that tolerate other weed killers. The Environmental Protection Agency is set to approve plans by Dow AgroSciences to sell soybean seeds that tolerate not only glyphosate, but a much older herbicide, 2,4-D, and a third widely used herbicide, glufosinate. Monsanto hopes to market soybeans and cotton next year that resist dicamba.
Dr. Mortensen and others say the companies are simply repeating the history that made palmers resistant to glyphosate. He says natural solutions, like planting what are known as cover crops that keep light from reaching germinating palmers, may cost more but are also effective.
Mr. Harper said he believes Dr. Mortensen is right. He also said he cannot wait for Monsanto and Dow to begin hawking their new soybeans anyway.
“I’m not stupid. I know you can only ride a pony so far,” he said. “It’ll probably take another 10 years before palmer becomes a real big problem again. But that just brought me 10 years I didn’t have.”
A version of this article appears in print on August 12, 2014, on page A11 of the New York edition with the headline: Invader Batters Rural America, Shrugging Off Herbicides. Order Reprints|Today’s Paper|Subscribe
Source: New York Times