Sustainable Agriculture Literature Review - Boulder County

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More recently, crops are being developed with stacked traits, also referred to as stacked
genes. Stacking traits allows a crop to contain a variety and combination of traits including
herbicide tolerant and insect resistance traits. 573 Other common traits incorporated and
stacked in transgenic crops include disease resistance, high pH tolerance, and several
nutritional, taste, texture, and shelf-life characteristics. 574 Gene stacking is becoming more
common, particularly in corn and cotton varieties. For example, nine percent of corn and
34 percent of cotton grown in the U.S. in 2005 were planted with stacked-gene varieties
(Figure 28). 575 Other studies reveal an increasing trend for stacked genes occupying a
growing percentage of GE crops worldwide, though specific percentages for Colorado
could not be obtained. 576
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Figure 28: Percentages of U.S. 2005 Crop Acreage Planted to Insecticidal,
Herbicidal, and Stacked-Gene Varieties.
The Economic Research Service (ERS) of the United States Department of Agriculture
(USDA) published a report in 2007 based on research collected and experiences gained
with transgenic crops during the first decade of cultivation in the U.S. spanning the years
1996-2005. 577 These authors concluded that transgenic crops could have environmental
benefits due to generally decreased pesticide usage and stimulation of soil conservation
practices. 578
The reductions in quantities of herbicide active ingredients applied to GE herbicideresistant
crops have shown decreases averaging 25-33 percent of overall use, according
to a study conducted by Sankulat et al. 579 A separate study by Brookes and Barfoot, 580
found a more modest decrease in pesticide usage averaging 6.3 percent. The authors
used existing data on the farm-level impacts of transgenic crops to calculate the economic
and environmental effects of all transgenic crops that had been cultivated over the nineyear
period of 1996–2004. The crops evaluated included herbicide resistant soybeans,
corn, cotton, and canola, as well as insect-resistant corn and cotton. The average
reduction varies between 2.5 percent for herbicide-resistant corn and 14.7 percent for
insect resistant cotton.
While GE crops reduce the overall use of pesticides, they often increase the use of a
specific type of pesticide for which the transgenic variety has been engineered to resist. 581
As shown in Graph 20, a variety of herbicide resistant (in this case glyphosate) soybeans
have reduced the overall quantity of non-glyphosate herbicides, but greatly increased the
use of glyphosate. 582 This example is similar to other transgenic varieties, where overall
pesticide use is reduced but applications of a single pesticide increased. This increased
reliance and use of a specific pesticide has raised concern from many researchers about
the increased development of resistant pests and in some cases the need for additional
pesticides to combat the newly resistant pest varieties. 583
As shown in Graph 20, transgenic crop varieties can reduce overall pesticide use and, to a
lesser extent, provide greater yields and increased returns. The extent of these benefits
depends greatly on the local conditions and farm operation as shown by the varying
results presented.
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