Increased Pesticide Use and Resistant Weeds -The Troubling Legacy of GE Crops

Washington, DC–(ENEWSPF)–October 3, 2012.  A study published this week by Washington State University’s research professor Charles Benbrook, PhD, finds that the use of herbicides in the production of three genetically engineered herbicide-tolerant crops -cotton, soybeans and corn- has actually increased, contrary to industry claims that the technology would reduce pesticide applications. While Dr. Benbrook’s analysis is the first peer-reviewed, published estimate of the impacts of genetically engineered (GE) herbicide-tolerant crops on pesticide use, scientists have been raising the alarm over the mounting numbers of herbicide resistant weeds.


This herbicide resistance finding, which contradicts chemical industry claims, is based on an exhaustive analysis of publicly available data from the U.S. Department of Agriculture’s National Agriculture Statistics Service. In the study, “Impacts of genetically engineered crops on pesticide use in the U.S. — the first sixteen years,” which appears in the peer-reviewed journal Environmental Sciences Europe, Dr. Benbrook writes that the emergence and spread of glyphosate-resistant weeds is strongly correlated with the upward trajectory in herbicide use. Marketed as Roundup and other trade names, glyphosate is a broad-spectrum systemic herbicide used to kill weeds. Approximately 95 percent of soybean and cotton acres, and over 85 percent of corn, are planted to varieties genetically engineered to be herbicide tolerant. The annual increase in the herbicides required to deal with tougher-to-control “superweeds” on cropland planted to GE cultivars has grown from 1.5 million pounds in 1999 to about 90 million pounds in 2011.

“Resistant weeds have become a major problem for many farmers reliant on GE crops, and are now driving up the volume of herbicide needed each year by about 25 percent,” Dr. Benbrook said.

According to the study, the emergence and spread of glyphosate-resistant weeds is by far the most important factor driving up herbicide use on land planted to herbicide-tolerant crops. Glyphosate-tolerant weeds were practically unknown before the introduction of Roundup-tolerant crops in 1996. But heavy reliance on the herbicide Roundup, whose active ingredient is glyphosate, has placed weed populations under progressively intense and unprecedented selection pressure, triggering a perfect storm for the emergence of glyphosate-resistant weeds. In general, in regions of the U.S. where Roundup-tolerant crops dominate, there are now evolved glyphosate-resistant populations of economically-damaging weed species. Resistant species like ryegrass and horseweed have been found in crop and non-crop areas, and now grow robustly even when sprayed with four times the recommended quantity of Roundup.

Scientists from USDA’s Agricultural Research Service (ARS) have noted that the relatively rapid evolution of glyphosate-resistant weed populations provides further evidence that no herbicide is invulnerable to resistance, and new weed management systems involving GE crops must be evaluated for the potential to create resistant species. Evidence suggests that GE corn plants can cross-pollinate non-GE corn plants beyond 200 meters. In order to limit gene flow between plant species several “best practice methods” are employed, such as maintaining isolation distances to prevent pollen movement from GE sources; planting border or barrier rows to intercept GE pollen; employing natural barriers to pollen, and field monitoring. However it can be concluded that these efforts are not effective, given the spate of genetic contamination and resistant weeds.

Herbicide-tolerant crops worked extremely well in the first few years of use, Dr. Benbrook’s analysis shows, but over-reliance have led to shifts in weed communities and the spread of resistant weeds that force farmers to increase herbicide application rates, spray more often, and add new herbicides that work through alternate modes of action into their spray programs. The study determined that herbicide-tolerant crop technology has led to a 527 million pound increase in herbicide use in the U.S. between 1996 and 2011, while Bacillus thuringiensis (Bt) crops have reduced insecticide applications by 123 million pounds. Overall, pesticide use increased by an estimated 404 million pounds, about 7%. Meanwhile, insects are beginning to show resistance to Bt-incorporated plants, jeopardizing a biological control that is sparingly used in organic production.

Dr. Benbrook concludes that, contrary to often-repeated claims that today’s genetically-engineered crops have and are reducing pesticide use, the spread of glyphosate-resistant weeds in GE weed management systems has brought about substantial increases in the number and volume of herbicides applied. Farmers have become increasingly critical of both GE seed (as it goes up in price) and herbicides like Roundup, as “superweeds” become prevalent in treated fields. The growth of pigweed, which can quickly reach widths of six inches at the stalk, and other glyphosate-resistant species increases farmers reliance on more high-risk herbicides, including 2,4-D, dicamba and paraquat, and has resulted in a return to hand harvesting and even the abandoning of fields. Dow AgroSciences and Bayer CropScience recently petitioned the USDA to deregulate 2,4-D GE corn and soybeans in order for 2,4-D and other herbicides to be used to tackle weeds resistant to glyphosate. However, according to Dr. Benbrook, if new GE forms of corn and soybeans tolerant of 2,4-D are approved, the volume of 2,4-D sprayed could drive herbicide usage upward by another approximate 50%.

Earlier this year, Beyond Pesticides wrote to USDA that the introduction of these new varieties of GE crops was “severely misguided and lacking forethought.” Arguably, by introducing 2,4-D GE corn into the environment, a new generation of resistant weeds will develop, leaving a legacy of “superweeds” resistant to both glyphosate, 2,4-D, and others, and a retrogression to even more toxic herbicides to control these weeds. 2,4-D, which constituted half of the ingredients in “Agent Orange,” used to defoliate forests and croplands in the Vietnam War, is a chlorophenoxy herbicide. Scientists around the world have reported increased cancer risks in association with its use, especially for soft tissue sarcoma and malignant lymphoma.

The prevalence of glyphosate-tolerant crops has also contributed to the high rates of glyphosate contamination in the environment. In 2002, the U.S. Geological Survey (USGS) collected 154 water samples from 51 streams in nine Midwestern states and glyphosate was detected in 36% of the samples, and aminomethylphosphonic acid or AMPA (a degradation product of glyphosate) was detected in 69% of the samples. Glyphosate and its formulated end-use products have been proven to be toxic to aquatic organisms and can be “extremely lethal” to amphibians in concentrations found in the environment. A 2012 study found that Roundup, in sublethal and environmentally relevant concentrations, caused two species of amphibians to change their shape by interfering with the hormones of tadpoles, and potentially many other animals.

This is not the first time that Dr. Benbrook has reported on the increased use of pesticides in the wake of increasing GE crops. In 2009, he wrote, “Impacts of Genetically Engineered Crops on Pesticide Use in the United States: The First Thirteen Years,” which first explored the impact of the adoption of GE corn, soybean, and cotton on pesticide use in the U.S. At the time, it was reported that GE crops were responsible for an increase of 383 million pounds of herbicide use in the U.S. over the first 13 years of commercial use of GE crops (1996-2008). The report identified, and discussed in detail, the primary cause of the increase–the emergence of herbicide-resistant weeds. Another 2009 report by the Union of Concerned Scientists, A Failure to Yield: Evaluating the Performance of Genetically Engineered Crops, reached similar findings.

Noteworthy is that while herbicide use has climbed, insecticide use has dropped. The adoption of GE corn and cotton that carry traits resistant to insects has led to a reduction in insecticide use, even though resistant insects like the corn rootworm have increased in numbers. However, this may be about to change since farmers in the Midwest are seeing severe rootworm damage in fields planted in Monsanto’s Bt corn, which was engineered to thwart these very same voracious bugs, now resistant to Bt. And in 2010, Monsanto also acknowledged that in industrial-agriculture regions of India, where Monsanto’s Bt cotton is a dominant crop, the cotton-attacking bollworm had developed resistance. Earlier this year, a group of 22 prominent entomologists, including researchers from land grant institutions in the Corn Belt and the USDA’s Agricultural Research Service (ARS), submitted formal comments to the U.S. Environmental Protection Agency that cast doubt on the future viability of certain varieties of GE Bt corn.

Currently, there are commercially available Roundup-tolerant seed varieties for corn, soybeans, canola, sorghum, and cotton, in addition to sugar beets, and recently USDA-allowed Roundup-tolerant alfalfa. Due to serious questions regarding the integrity of USDA’s environmental evaluations, public interest groups, led by the Center for Food Safety and including Beyond Pesticides, have filed suit against the agency to stop its full deregulation of GE alfalfa. For more on genetically engineered agriculture read Beyond Pesticides’ article “Ready or Not, Genetically Engineered Crops Explode on Market.“

Sources: Washington State University News Room

All unattributed positions and opinions in this piece are those of Beyond Pesticides.