A genetically engineered grass expected to hit U.S. markets without government review could speed the evolution of hard-to-control weeds, and perhaps require a return to toxic herbicides scrapped decades ago.

On July 1 — a Friday afternoon, a time usually reserved for potentially controversial news — the U.S. Department of Agriculture announced that Scotts Miracle-Gro’s herbicide-resistant Kentucky bluegrass would be exempt from tests typically required of transgenic crops.

Scotts Miracle-Gro is the largest U.S. retailer of grass seed, and the modified grass could be widely used in residential lawns. It’s resistant to glyphosphate, a front-line herbicide known commercially as Roundup.

The grass will survive extra doses of Roundup, allowing more than usual to be applied. That’s the problem, said agricultural biotechnology expert Douglas Gurian-Sherman of the Union of Concerned Scientists.

“The more a chemical is used consistently, the more likely that somebody’s weeds will become resistant. That’s standard, agreed-upon science,” said Gurian-Sherman. “The way that Roundup is used because of transgenic crops exacerbates that problem.”

Herbicide resistance evolves in much the same way as antibiotic resistance: When a weed- or bug-killing compound is applied, any weeds or bugs lucky enough to be genetically resistant will have the best chance to survive and reproduce.

Many crop plants are already engineered to be Roundup-resistant, and heavy use of the herbicide appears to have fueled the evolution of dozens of Roundup-resistant weed strains. They’re a major threat to agriculture in parts of the United States, virtually uncontrollable except by hand-pulling or a return to toxic, decades-old herbicides that the relatively benign Roundup had replaced.

Pigweed growing in a soybean field. Since the introduction of Roundup-ready soy, Roundup-resistant pigweed has become a major problem. (Image: pawpaw67/Flickr)

Compared to pigweed that can grow three inches each day in soybean fields, Roundup-resistant lawn weeds would be a nuisance rather than an economic threat. But just as superweeds have pushed farmers to bring back toxic herbicides, so might they push homeowners and landscapers.

“We’re burning out Roundup and going back into the past,” said Gurian-Sherman. “The same kind of thing could happen in residential use.”

Another potential problem is the spread of Roundup resistance into related strains of bluegrass, said plant geneticist Norman Ellstrand of the University of California, Riverside.

“I don’t know what other bluegrass species it’s cross-compatible with, but I can say with 98 percent certainty that it’s cross-compatible with some,” said Ellstrand. “If this plant grows and flowers at the same time as other bluegrass, they’ll flourish. You’ll have a new incidence of herbicide resistance getting into the wild.”

Whereas Kentucky bluegrass is popular for lawns, it’s not always welcome. Other members of its 500 species-strong genus are considered weeds.

A lesson can be taken from the unintentional escape of genes from rice bred for resistance to the Clearfield herbicide, said Ellstrand. “Now you have a very bad, weedy rice in Costa Rica that’s resistant to the herbicide,” he said. “It doesn’t happen easily with rice. If it happens with rice, it will happen with bluegrasses.”

Another species of Roundup-resistant grass developed by Scotts Miracle-Gro for golf courses was nixed by the USDA because of fear that resistance would spread to related pest species, noted Ellstrand. “The U.S. Forest Service waded in and said, ‘We don’t want it,’” he said.

Had the the Department of Agriculture decided to treat Roundup-ready bluegrass as a genetically modified plant, extra assurance of its environmental safety would have been demanded. But they decided not to because it fit through a loophole.

Genetically engineered plants are technically designated for regulation according to methods used to insert and activate new genes. Earlier methods used bacteria, which triggered pest-related clauses of the USDA’s Plant Protection Act. But the Roundup-ready bluegrass was made with a so-called gene gun. No bacteria were involved, and the law’s fine print was satisfied.

“By all definitions of genetic engineering, that’s genetic engineering. But it totally escapes the U.S. regulatory framework,” Ellstrand said.

According to Scotts Miracle-Gro spokesman Lance Latham, the USDA’s decision “allows us to move forward with field tests. It’s a first step. It’s our hope that testing will continue our advancement to develop grass seed that is even more sustainable.”

Image: Anne Homyak/Flickr

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