HARD TO RESIST: Glyphosate was developed to be used with genetically engineered seeds that can resist the herbicide. But repeated use of the chemical has decreased its effectiveness, researchers say. Image: ISTOCKPHOTO/Purdue9394
Resistance to glyphosate, a herbicide more popularly known as Roundup, has been rising among weeds across the American Southeast that are growing among genetically engineered crops, according to a report released today by the National Research Council.
"Weed resistance is so bad in Georgia that GE cotton is no longer being used as much," said LaReesa Wolfenbarger, a co-author of the report and associate professor of biology at the University of Nebraska. The committee presented its work at the National Academy of Sciences today.
The resistance could be a big problem and negate any economic or environment- and climate-related benefits of genetically engineered crops, said David Ervin, chairman of the committee and a professor of environmental management and economics at Portland State University.
"This problem is growing, it is real, and it is going to get worse," he said.
Glyphosate is the most popular herbicide in America, and it targets a broad spectrum of weeds while being only mildly toxic to animals. It breaks down easily in the soil, and as such is less damaging than other herbicides.
Monsanto developed glyphosate in the 1970s to be marketed together with its Roundup Ready genetically engineered seeds that can resist the herbicide. But repeated use of the chemical has decreased its effectiveness, according to Wolfenbarger.
Of the 10 species of weed that have become resistant, eight have developed resistance because of the prevalence of Roundup Ready crops in the area, she said.
There has been little evidence of resistance developing to the insect-resistance Bt trait, according to the report. The Bt gene from the bacterium Bacillus thuringiensis is a better tactic for killing insects than spraying broad spectrum insecticides that can kill indiscriminately, targeting honeybees and other pollinators as well as pests, said Wolfenbarger.
Little research on long-term impacts
The evolution of resistance calls for a more diverse farm management practice, said the scientists. Practices such as crop rotation, using herbicides with different modes of action, and precision agricultural techniques are all necessary, according to Wolfenbarger.
"We need better management to increase the longevity of weed resistance technology," said Ervin. "GE crops have provided multiple benefits to farmers."
The committee also faced a frustrating lack of research into the impacts and effects of GE crops in America 14 years after they were first introduced. Nearly half the acreage in the country is planted with GE varieties today, accounted for by three major crops -- corn, soybean and cotton.
The report found that GE crops generally had fewer adverse effects on the environment compared to conventional farming practices using non-GE crops. This is because farms growing GE used less tilling for weed removal and0 less pesticide and had less soil erosion.
Better soil quality stops pesticides from contaminating waterways and causing the algal blooms that are a hallmark of less-sustainable agricultural practice. But no one has monitored the waterways so far to see whether the positive impact has in fact occurred, according to the report.
Other benefits of GE crops tend to be economic, with farmers having to invest less in buying pesticides, better worker safety and greater flexibility in farm management.