Genetically engineered varieties of soybeans, corn, and
cotton have been available commercially since 1996. Since then,
their rate of use by U.S. farmers has climbed most years, including
2004. For the most part, farmers have adopted herbicide- tolerant
(HT) varieties, which help control weeds, at a faster pace than
insect-resistant varieties, which help control insects.
Weeds are such a pervasive pest for soybeans, corn, and cotton that
over 90 percent of planted acreage for each crop was treated with
herbicides in recent years. Crop varieties with HT genes can survive
certain potent herbicides that previously would have destroyed the
crop along with the weeds, giving farmers who adopt HT varieties
a powerful new tool to control weeds. Acreage share for HT soybeans,
which reached 85 percent of U.S. soybean acreage in 2004, has expanded
more rapidly than acreage shares for HT varieties of cotton and
corn. Farmers’ adoption of HT soybeans has been widespread
among major growing States, ranging in 2004 from 75 percent in Michigan
to 95 percent in South Dakota. Acreage share for HT cotton has also
expanded rapidly, reaching 60 percent in 2004. In contrast, acreage
share for HT corn reached only 18 percent in 2004, but this is still
an increase from 15 percent in 2003.
Insect-resistant crops contain a gene from a soil bacterium,
Bacillus thuringiensis (Bt), which produces a protein toxic to specific
insects. Acreage shares for Bt cotton and corn are lower than those
for HT soybeans and cotton and vary much more across producing States,
with adoption more concentrated in areas with high infestations
of targeted pests. Farmers planted Bt cotton—which controls
tobacco budworm, bollworm, and pink bollworm—on 46 percent
of cotton acreage in 2004. Acreage share ranged from 13 percent
in California to 86 percent in Louisiana. Bt corn, originally developed
to control the European corn borer, was planted on 32 percent of
corn acreage in 2004, up from 29 percent in 2003 and 24 percent
in 2002. These recent increases in acreage share may be largely
due to the commercial introduction in 2003/04 of a new Bt corn variety
that is resistant to the corn rootworm, a pest that may be more
destructive to corn yield than the European corn borer.
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