The USDA has deregulated two new genetically engineered crop varieties, allowing farmers to grow the transgenic cotton and soybeans without restriction.
So far in 2011, the agency has permitted the commercialization of seven genetically engineered crops, up from two in 2010 and three in 2009.
The transgenic cotton cultivar - TwinLink - was developed by Bayer CropScience to withstand common larvae pests like the bollworm, tobacco budworm and fall armyworm.
The crop relies on two different genes from the soil bacteria Bacillus thuringiensis, or Bt, to reduce the likelihood of pests becoming resistant to its "insecticidal" properties, according to USDA.
The variety also incorporates genes from another soil bacteria that render the crop tolerant to glufosinate herbicides, helping to discourage weeds that have grown resistant to other chemicals, according to the agency.
The USDA completed an environmental assessment, which found the cultivar isn't likely to pose a plant pest risk, won't cross with "compatible wild relatives" and doesn't have the capability of becoming a weed.
Biotech critics like the Center for Food Safety are critical of the trend toward more herbicide-resistant transgenic crops.
"The problem is you're likely to get weeds also resistant to glufosinates," said Bill Freese, science policy analyst for the group. "It's the whole pesticide treadmill thing."
Biotech companies are developing new genetically engineered crops that are tolerant of additional herbicides due to the "epidemic" of weeds that are resistant to glyphosate, a popular chemical, he said.
The Center for Food Safety worries this trend will result in the increased usage of more dangerous chemicals, Freese said. "Glufosinate is definitely more toxic than glyphosate."
The other biotech crop recently deregulated by USDA is a soybean variety that is resistant to insects like the bean shoot borer, Epinotia aporema, which is a severe threat to soybeans in South America, according to the agency.
Areas in the South are afflicted by similar pests, but due to the high variability of insect pressure it's unlikely that the new variety, developed by the Monsanto Co., will attain more than a 15 percent market share domestically, USDA said.
Freese said he's concerned by reports that Brazil - the largest potential market for the cultivar - will not require refuge requirements for farmers. With some biotech crops, farmers must plant "refuges" of non-transgenic cultivars to slow down pest tolerance to insect-resistant plants.
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