Saturday, Jul 18, 2020, 3:17 pm Bayer Engineered a New Corn Seed That’s
Resistant to Five Herbicides. But How Long Will It Work? By Johnathan
Hettinger <>


A farmer sprays the herbicide glyphosate on a corn field.   (Photo by
Jean-Francois Monier / AFP via Getty Images)

*Editor's Note: This story was originally published by the Midwest Center
for Investigative Reporting

A new genetically engineered corn seed designed by Bayer to be sprayed by
up to five herbicides could represent the future of farming, providing
growers with more pesticides to combat the problem of weed resistance.

But for how long? That’s the question raised by weed scientists, who say
farmers need to start switching to non-chemical options to keep weeds under

Over the past 50 years, weed resistance has become a significant problem
for agriculture in the U.S., with more than 165 unique species of weeds
becoming resistant to chemicals. The problem has increased significantly
since the introduction of genetically modified crops and use of
accompanying herbicides in the 1990s.

The new seed, which Bayer has petitioned the U.S. Department of Agriculture
for approval, could be sprayed by glyphosate, glufosinate, dicamba, 2,4-D
and quizalofop, giving farmers multiple options for weed control.

Bayer spokeswoman Susan Luke said in an email that, pending regulatory
approvals, the company plans a full commercial launch of the seed later
this decade.

“We expect HT4 to be widely used – and growers continue to ask for
additional crop protection tools to help manage tough-to-control weeds.
This product will offer growers more options to manage broadleaf weeds in
corn and will provide growers increased flexibility and another tool in the
crop protection toolbox,” Luke said.

Corn is the most bountiful crop grown in the United States
making up about 92 million acres of farmland, an area about the size of
Minnesota or Michigan; about a third of the crop is used for animal feed,
about a third is used for ethanol and the rest is split between human food,
beverages, industrial uses and exports. About 90 percent of corn grown in
the U.S. is genetically modified, according to the USDA

The product comes at a time when Bayer, which acquired agribusiness giant
Monsanto in 2018, and its pesticides are under scrutiny.

In June, Bayer announced a $10 billion settlement of claims that
glyphosate, the active ingredient in Roundup, causes cancer. The company
also announced a $400 million settlement of claims that dicamba, a
herbicide sold by Bayer and German agribusiness company BASF, has drifted
and harmed thousands of other farmers.

By purchasing Monsanto, Bayer acquired some of the most popular cropping
systems in the U.S.

Monsanto’s Roundup Ready crops, engineered to be resistant to the herbicide
Roundup, quickly became ubiquitous after being introduced in the 1990s.
Glyphosate, the active ingredient, is the most commonly used herbicide in
the U.S., but as the amount sprayed in crops increased 40-fold between 1992
and 2016
the number of weeds resistant to glyphosate grew. Over the past 25 years,
the number of weeds resistant to glyphosate has increased from zero to more
than 45, according to the International Survey of Herbicide Resistant Weeds

In response, agribusiness companies have released crops engineered to be
resistant to other herbicides: Monsanto launched its Roundup Ready II
crops, engineered to be resistant to glyphosate and dicamba; BASF launched
its Liberty crops, designed to be resistant to glyphosate and glufosinate;
Corteva Agriscience, formerly DowDupont, released Enlist crops, designed to
be resistant to glyphosate, 2,4-D and quizalofop.

The new Bayer technology combines all of these technologies into one. The
new product is not designed to be sprayed by all five weed killers at once,
but instead to help streamline the current agricultural system, allowing
seed dealers to carry one seed that gives farmers a choice on which
combination of weed killers they want to spray.

“It’s not a big revolution. It’s the way things are moving,” said Robert
Hartlzer, a weed science professor at Iowa State University.

This phenomenon is often called “the pesticide treadmill” — as more weeds
develop resistance to more herbicides, new and better herbicides are

The acceleration seems to be getting faster and faster, said Kristin
Schafer, executive director of the Pesticide Action Network. PAN is
organizing citizens to submit comments against the new Bayer technology,
saying the cropping system would be more benefited by switching to crop
rotations, more biodiversity on the farm and increased soil health.

“This five-trait corn is absolutely the opposite direction of the way we
need to be going,” Schafer said.

Some weeds are already starting to show signs of resistance to dicamba
which has increased significantly in use since Monsanto introduced new
cotton and soybean seeds resistant to the herbicide beginning in 2015.
Dicamba has also caused widespread damage to the environment
it is harder to control.

Hartzler warned that weeds are quickly outpacing technological
developments. Weeds have already developed resistance to each of the
herbicides included in the technology, though they are still very effective
across the United States.

“It’s really going to be a short-term fix, but at this point in time, it’s
what fits the current production system best,” Hartlzer said.

Aaron Hager, a weed science professor at the University of Illinois, found
in a 2015 study that using multiple herbicides to kill weeds is better at
delaying resistance than switching from one herbicide one year to a
different the next. Bayer pointed the Midwest Center to that study and said
the new seed will help delay resistance.

But Hager said the way that weeds are resistant to herbicides is changing.

Herbicides work by targeting a specific mechanism in a plant and disrupting
that mechanism. For the past 30 years, weeds have largely started to
develop resistance at the target site, shifting the way they grow and no
longer allowing herbicides to bind to the plant.

But increasingly, plants have started to develop metabolic resistance,
which is when the plant’s internal mechanisms are able to metabolize
herbicides into non-toxic products, making them ineffective. The mechanism
is similar to crops that are able to sustain being sprayed by herbicides.

“We’re in another era now,” Hager said. “We’re trying to understand what
has changed and allows them to function more like the crop.”

With metabolic resistance, weeds can develop resistance to herbicides that
they haven’t been exposed to before, Hartzler said.

Bayer said that these chemicals are needed. Even with best practices, corn
can see a 52 percent yield loss without a herbicide being sprayed, according
to a study by the Weed Science Society of America
Hager said that farmers won’t stop using chemicals, but they can use them
along with other options.

Both Hager and Hartzler said they are recommending farmers increasingly use
non-chemical options. Hartzler said places like Australia are starting to
use combines that can help destroy weed seeds, so they don’t continue to

“I know that it’s going to change in the relatively near future simply
because even the addition of these new herbicide traits is not going to
solve the resistance problem,” Hartzler said.

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