As a follow-up to Tom Philpott's post about genetically modified crops (also known as transgenic or genetically engineered crops), I thought I'd post some data on transgenic crop adoption in the United States. Because products made from transgenic crops are never labeled, it is probably not well known that over 70 percent of the corn acreage, around 90 percent of the soybean acreage and almost 90 percent of the cotton acreage is planted with transgenic varieties. These statistics and the figure below are drawn from a report from the USDA called Adoption of Genetically Engineered Crops in the U.S.
In the figure below, the acronym HT stands for "herbicide tolerant" (the plant is impervious to a specific class of herbicide, like Monsanto's Roundup) and the term Bt indicates that the plant carries genes from the soil bacterium Bacillus thuringiensis (which make the plant toxic to certain insects). The genes of some plants are modified to contain herbicide tolerance and Bt genes; these are called "stacked gene" varieties. Note that when the USDA calculated the quantity of HT or Bt acreage, they included the stacked gene varieties in both categories (that is why the sum of HT cotton and Bt cotton is greater than 100 percent). Fortunately, the Excel spreadsheet included with the report has a section with the percentage of acres planted with any type of transgenic crop — in 2007 it was 73 percent of corn acres, 87 percent of cotton acres, and 91 percent of soybean acres.
Here are more comprehensive definitions of Bt and HT from the USDA Glossary on Genetically Engineered Crops:
Bt crops are genetically engineered to carry the gene from the soil bacterium Bacillus thuringiensis. The bacteria produces a protein that is toxic when ingested by certain Lepidopteran insects. Crops containing the Bt gene are able to produce this toxin, thereby providing protection throughout the entire plant.
Herbicide-tolerant (HT) crops were developed to survive certain herbicides that previously would have destroyed the crop along with the targeted weeds, and allow farmers to use them as postemergent herbicides, providing an effective weed control. The most common herbicide-tolerant crops (cotton, corn, soybeans, and canola) are Roundup Ready (RR) crops resistant to glyphosate, a herbicide effective on many species of grasses, broadleaf weeds, and sedges. Other genetically modified herbicide-tolerant crops include Liberty Link (LL) corn resistant to glufosinate-ammonium, and BXN cotton resistant to bromoxynil.