Accessibility links

New GMO Crops May Raise Herbicide Use

FILE - Soybean plants that were grown from soybean seeds genetically engineered to resist a common weed killer in an undated photo released by Dow AgroSciences.

FILE - Soybean plants that were grown from soybean seeds genetically engineered to resist a common weed killer in an undated photo released by Dow AgroSciences.

A new generation of genetically modified organisms has taken a step toward the market, promising farmers better control of especially troublesome weeds.

But critics say those weeds are a byproduct of the first round of GMOs, and this new round will dramatically increase the use of a more problematic herbicide that environmentalists say may raise health concerns.

A branch of the U.S. Department of Agriculture has recommended approval of two varieties of soybean and one type of corn developed by Dow AgroScience that can withstand treatment with two popular weed killers: glyphosate, sold under the name Roundup, and 2,4-D, an herbicide that’s been around since the 1940s.

The aim is to give farmers a tool to fight the growing number of weeds that Roundup no longer kills.

Glyphosate-resistant crops first hit the market in the mid-1990s, with seed and chemical giant Monsanto’s “Roundup Ready” crops.

“That was monumental in agriculture. Just monumental,” said University of Georgia weed scientist Stanley Culpepper.

Farmers could apply “one of the most effective, economical and environmentally-friendly herbicides on the planet right over the top of the crop,” he said. “And you could do this without damaging the crop. And at that time, that was simply unheard of.”

Plus, farmers no longer needed to till their fields to control weeds. Leaving the soil undisturbed makes the soil richer in organic matter, which improves water retention and reduces pollution from runoff. And it means fewer trips on the tractor, saving on fuel costs.

Farmers' dream, or nightmare?

They were a farmer’s dream. Herbicide resistant crops quickly came to dominate American agriculture. Last year, they made up 85 percent of the corn, 82 percent of the cotton and 93 percent of the soybeans planted in the U.S.

There was a downside.

“To some degree, it allowed us to be a little too lazy,” Culpepper said.

Farmers used Roundup and nothing else to control their weeds. And they used it over and over again, season after season.

It wasn’t long before weeds were shrugging off the herbicide.

“It’s really Darwinian evolution on steroids,” said senior scientist Doug Gurian-Sherman with the environmental group Union of Concerned Scientists.

By 2012, nearly half of U.S. farmers told a private survey they had Roundup-resistant weeds. More than 24 million hectares were infested, nearly double the area from 2010.

Any weed will suck water, nutrients and light from a neighboring crop plant. But for cotton growers in Georgia, palmer amaranth is their nightmare weed. On a good day it can grow five centimeters. It can reach three meters tall. One plant can produce half a million seeds.

“He’s bad. He’s as bad a weed as there ever was,” said Jack Royal, an independent consultant who has been advising farmers on weed control for 36 years.

Controlling this bad weed has required big changes. Farmers with infested fields are going back to older, less benign herbicides. They till their fields more often, which leads to more erosion, decreases soil quality and raises farmers’ fuel costs. Many have even had to resort to hiring help to pull out weeds by hand.

But it’s working. Partly.

“We’re doing extremely well in controlling palmer amaranth,” Culpepper said. “That’s the good news.”

The bad news: weed control that used to cost cotton farmers less than $10 a hectare now costs $30 to $40.

“Bottom line is, we’re not economically sustainable,” Culpepper said.

Next generation of GMOs

That’s where Dow AgroScience’s new Enlist seeds come in.

Farmers planting these seeds would be able to spray their fields with both glyphosate and 2,4-D, which still kills palmer amaranth and many other glyphosate-resistant weeds, without damaging their crops.

“Enlist will be a tool to help address the significant weed control problems that farmers are facing today,” Dow said in a statement.

Use of 2,4-D is likely to double or more if Enlist seeds are approved, according to some estimates.

But Gurian-Sherman recalls that one of the arguments in favor of Roundup-Ready GMOs when they were introduced was that they would allow farmers to use newer, safer herbicides.

“That whole argument is going down the tubes,” he said.

Environmentalists point to studies linking 2,4-D to cancer, hormone disruption and genetic mutations.

But the U.S. Environmental Protection Agency has said the evidence is not conclusive and declined one group’s petition to remove it from the market.

The herbicide has another well-known weakness, Royal said. “We’ve used a lot of 2,4-D products. Drift has always been a major problem.”

And when the herbicide drifts, it can damage or kill plants downwind.

That’s potentially a big problem for states like Georgia, with large acreages of commodity crops like cotton and corn alongside farms of fruits, vegetables and nuts.

Dow has produced new formulations aimed at reducing drift. And Culpepper says the industry has made tremendous advances in nozzle designs that reduce fine particles.

Eventually, though, weeds will likely develop resistance to 2,4-D, too, Gurian-Sherman said.

Alternative approaches to weed control

“There are other ways to control weeds,” he added. For example, cover crops that out-compete weeds are showing promise but need more research.

“We know these approaches can be highly productive and lucrative,” but, he added, “the research agenda for decades neglected these sustainable practices in favor of industrial agricultural practices.”

Royal agrees cover crops are one weapon in the weed control arsenal. He also sees a role for the new seeds.

But, he said, one thing the Roundup Ready experience shows: “Some good new technology may come along, but there are no silver bullets.”

A final decision on approval of the new GMO seeds is expected later this year.
  • 16x9 Image

    Steve Baragona

    Steve Baragona is an award-winning multimedia journalist covering science, environment and health.

    He spent eight years in molecular biology and infectious disease research before deciding that writing about science was more fun than doing it. He graduated from the University of North Carolina at Chapel Hill with a master’s degree in journalism in 2002.