Sustainable Agriculture Literature Review - Boulder County

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Graph 20: Herbicide Use on Soybeans in the U.S. 584
The review of the first decade of transgenic crops by the ERS USDA found that the
currently available GE crops are not guaranteed to increase the yield potential. They found
that the yield might decrease if the varieties used to carry the herbicide-tolerant or insectresistant
genes are not the highest yielding cultivars. However, they found that when pest
infestation is high, GE varieties could help to prevent yield losses compared with non-GE
hybrids. 585
Herbicide Tolerance
Some GE Herbicide tolerant crops are engineered to tolerate high application rates of
glyphosate, an herbicide that is used to control weeds. For example, glyphosate-tolerant
soybean crops are able to tolerate twice the level of glyphosate application needed to
control weeds without negatively impacting the yields. A study done on per acre net return
of glyphosate-tolerant soybeans concluded that higher returns were a result of higher
yields and lower herbicide costs. Glyphosate-tolerant soybeans were shown to have
approximately a $6 per acre higher return than traditional varieties. They found that the
lower herbicide costs were enough to make up for the higher costs of seeds and
technology fees. 586
However, glyphosate-tolerant cotton does not show the same economic gains as
glyphosate-tolerant soybeans. Field studies found that there is little difference in yields
between using glyphosate-tolerant cotton and standard cotton. Although there were no
economic gains by using glyphosate-tolerant cotton, less total herbicides were used in this
study. Herbicide-tolerant corn showed no statistically significant difference in profit over
conventional varieties, but did find that less total herbicides were used. 587 While yields and
market prices vary depending on the HT crop, fewer herbicides are used on all; however,
they can also cause negative effects. Weed management and weed control have been
simplified by HT crops, but can lead to a decreased understanding of weed biology and
weed interactions, which could diminish the use of Integrated Pest Management (IPM)
practices. 588
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