Karen L. Werner
Soybeans genetically engineered to withstand applications of the herbicide glyphosate (also know as Roundup) need to be treated with more herbicides compared to conventional soybean varieties, a May 2 report from the Northwest Science and Environmental Policy Center stated. The genetically modified soybeans also produce fewer bushels per acre than other soybeans, the report concluded, based on university experimental trials.
"If reducing the pounds of herbicides applied per acre was among the important goals shaping U.S. soybean weed management systems in the 1990s, the introduction of Roundup Ready soybean varieties was a major step backward," according to the report. The title of the report is Troubled Times Amid Commercial Success for Roundup Ready Soybeans: Glyphosate Efficacy is Slipping and Unstable Transgene Expression Erodes Plant Defenses and Yields.
Many soybean herbicides are sold in "combination products" that contain two or three active ingredients, the report said, and many of these have been introduced to supplement weed control for Roundup Ready soybeans.
Representatives of Monsanto Co. of St. Louis--the developer of the soybean--and of the National Center for Food and Agricultural Policy took issue with the report's conclusions. No studies have shown an increase in pesticide use with the Roundup Ready soybeans, Monsanto's Harvey Glick told BNA May 2. Glick, leader of global biotechnology stewardship for Monsanto, said Roundup Ready soybeans continue to be an effective tool for farmers to remain competitive in a global market.
Roundup Ready soybeans allow farmers to spray a single broad-spectrum herbicide active ingredient glyphosate (Roundup) over growing soybeans to kill weeds.
Consultant Charles Benbrook, author of the report, said his work is the first that he knows of that analyzes U.S. Department of Agriculture (USDA) data at the "field level" for herbicide use in soybeans.
Benbrook said he conducted the analysis to correct "misinformation" he sees from the biotechnology industry and its advocates.
According to the report, although the "best-case" scenario Roundup Ready systems require less herbicide than the highest application rate conventional systems, most Roundup Ready soybeans will be treated with about 0.5 pounds per acre more herbicide than most conventional soybeans in 2001.
The report said one trend in herbicide use and Roundup Ready soybeans is that most farmers growing the genetically engineered soybeans apply one to three additional active ingredients, because of "slipping efficacy" of Roundup.
The "efficacy slip" in Roundup occurs because of an accompanying shift toward species of weeds that Roundup is not as effective on, Benbrook said.
Glick denied the existence of a drop in efficacy of Roundup and said Monsanto has done more than 500 "side-by-side" commercial field trials in four years, and there is a slight increase in yield with the Roundup Ready soybeans.
Nationally, in 1998, there were 65.7 million total acres of soybeans planted, with 36.7 million of them, or 55.8 percent, planted to conventional varieties, the report said.
About 25.4 million acres, or 38.8 percent of the total soybean acres planted in the country in 1998, were planted with Roundup Ready soybeans, and 3.5 million acres were planted with other herbicide-tolerant varieties, the report said.
The popularity of Roundup Ready soybeans has caused other herbicide makers to lower their prices, encouraging heavier reliance on herbicides, the report said.
On average soybean acres nationwide, farmers applied 1.17 pounds of herbicide active ingredient in 1998, with an average of 0.92 pounds of glyphosate per acre applied to 30.7 million acres, the report said. On Roundup Ready soybeans, an average of 1.22 pounds of herbicide per acre was applied, with 1 pound per acre of glyphosate.
Benbrook said the Roundup Ready soybeans produce 5 percent to 10 percent fewer bushels per acre, contrasted to otherwise identical varieties grown under comparable conditions. Changes to the soybeans (including decreased nitrogen fixation) due to application of Roundup can reduce their yield, the report added.
Fewer farmers will want to accept the trade-offs and costs involved with Roundup Ready soybeans, especially with yield decreases, Benbrook said.
According to Benbrook, there are three lessons to be learned from the rapid adoption of Roundup Ready soybeans, absent independent, nonindustry research. First, any biotechnology that increases reliance on one pest management tool, and especially one herbicide, "is headed for trouble."
Second, inserting genes into plants' metabolic pathways is a "risky proposition" that is likely to lead to unanticipated consequences, especially if plants are stressed by other factors, the report said.
Third, there was a lack of "independent" research on some consequences of the soybeans until "well after" regulatory approvals and widespread adoption, the report said.
Benbrook is based in Sandpoint, Idaho. Benbrook's center is a nonprofit research and policy center.
The report was based in part on 1998 herbicide use raw data from the Agriculture Department that have not been publicly available. These data were specially tabulated by USDA's Economic Research Service for Benbrook.
Benefits of Roundup
The report said there are more herbicides used on Roundup Ready crops than on other soybeans that rely on so-called low-dose chemicals. However, Leonard Gianessi of the National Center for Food and Agricultural Policy said the data on use of low-dose herbicides are deceptive.
A low-dose herbicide controls fewer types of weeds, and the use of additional herbicides are necessary. Therefore, they are not really "low-dose" herbicides when the other products are added in, Gianessi said.
The low-dose herbicides also are chemically active for up to four years in the soil, Gianessi said. Glyphosate disappears immediately in the environment because it binds to soil and soil microbes attack it, he said.
The low-dose herbicides present a challenge for sustainable agriculture because if farmers want to rotate from nonengineered soybeans to wheat after use of the low-dose products, for example, the herbicides still could damage the wheat, he said. Soybean growers have rejected low-dose herbicides because they have harmed the wheat, Gianessi said.
Weed Control Method
Contrary to Benbrook's report, Gianessi said low-dose herbicides work well if weeds are less than 2 inches tall, but not so well for larger weeds. Glyphosate kills weeds up to 6 inches tall, he said. It is crucial to look at the variable of weed control method, Gianessi said. Benbrook's report looks at yields in variety trials that compare different soybean varieties, but these trials do not have the variable of weeds, which are hand-pulled, Gianessi said.
These trials also do not consider the herbicide used to kill the weeds, he added.
The alleged "yield drag" of Roundup Ready soybeans is actually a "lag," and as the Roundup Ready soybeans are further developed, they are catching up to conventional crops, Gianessi said. Research by Gianessi's center indicates the yield disparity is more likely because of the need for additional "backcrossing" using conventional breeding techniques.
Benbrook's report also did not use 1999 data, which indicate herbicide use in pounds per acre decreased from 1998 to 1999, from 1.06 pounds per acre in 1998, to 1 pound per acre in 1999, Gianessi said.
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Last Updated on 5/14/01