Scott Harper, the weed expert at
Harper Brothers Farms in Indiana, inspected a soybean field for
invasive, herbicide-resistant weeds known as palmers.
Credit Daniel Acker for The
New York Times
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.”