Government regulators have approved a new generation of genetically engineered corn and soybeans. They're the latest weapon in an arms race between farmers and weeds, and the government's green light is provoking angry opposition from environmentalists.

The actual decision, at first glance, seems narrow and technical. The Environmental Protection Agency has announced it had "registered" a new weedkiller formula that contains two older herbicides: glyphosate (better known as Roundup) and 2, 4-D.

Versions of these weedkillers have been around for decades. But farmers in six Midwestern states will be allowed to use the new formula, called Enlist Duo, on their corn and soybeans. And that counts as big news.

Farmers will now be able to plant new types of corn and soybeans that have been genetically engineered by the biotech company Dow Agrosciences to tolerate doses of those two weedkillers. (The beauty of herbicide-resistant crops is that they make the herbicides exquisitely selective: They kill the weeds but not the crop.) So farmers can spray either glyphosate or 2, 4-D (or both) to wipe out weeds without harming their corn or soybeans.

And that may actually be one of the most significant developments the world of weedkilling in more than a decade.

Another similar new weedkilling combination of the chemical dicamba and genetically engineered, dicamba-resistant crops is awaiting government approval. Promoters of these new herbicide-crop combinations say they are a big step forward. Critics are calling them a mindless step into ever-increasing dependence on toxic chemicals.

There's demand for such technologies because the last great weed-fighting weapon is starting to fail. Over the past two decades, farmers have come to rely, to an extraordinary extent, on glyphosate paired with "Roundup Ready" crops. But an increasing number of weeds have now evolved resistance to glyphosate. Farmers have had to resort to weedkilling chemicals that are more costly and often harder to manage. Many of those chemicals can't be sprayed directly on crops because they'd kill them.

Environmentalists and critics of genetically engineered crops condemned the EPA's decision Wednesday, arguing that it leads farmers "further down the futile path of chemical dependency," in the words of Andrew Kimbrell from the Center for Food Safety. Mary Ellen Kustin, from the Environmental Working Group, said in a statement that "this continued arms race between chemical companies and superweeds is a threat to sustainable farming and public health. EPA's decision to up the ante of Roundup by approving Enlist Duo is unconscionable."

In fact, the EPA's green light to Enlist Duo did contain some unusual provisions that the agency could eventually use to restrict its use. The EPA is requiring that Dow monitor the use of the new herbicide, work with farmers to avoid overusing it and come up plans to fight weeds that become resistant to the new weedkiller. In addition, the EPA's approval of Enlist Duo is temporary, and will expire in six years.

On the same day that the EPA approved the new herbicide, the U.S. Department of Agriculture announced a new program aimed at fighting the problem of herbicide-resistant weeds. According to the USDA statement, this problem "will not be solved solely through the application of new herbicides." USDA scientists will carry out research on non-chemical ways to control weeds, such as cover crops, and promote their use among farmers.

Copyright 2021 NPR. To see more, visit https://www.npr.org.