Agriculture Reference
In-Depth Information
increased modestly in later years (figure 14a). Herbicide use on soybean farms
has been mostly constant since 1996, but increased slightly starting in 2002
and peaked in 2006
.
Herbicide use on corn fell from about 2.6 pounds per acre
in the early years of HT corn adoption to less than 2 pounds per acre in 2002
but increased moderately in recent years. Herbicide use on corn by HT
adopters increased from around 1.5 pounds per planted acre in both 2001 and
2005 to more than 2.0 pounds per planted acre in 2010, whereas herbicide use
by nonadopters did not change much (figure 14b). HT adoption likely reduced
herbicide use initially, but herbicide resistance among weed populations may
have induced farmers to raise application rates in recent years, thus offsetting
some of the economic and environmental advantages of HT corn adoption
regarding herbicide use.
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B
T
C
ROP
A
DOPTION AND
A
REAWIDE
P
EST
S
UPPRESSION
Hutchinson et al. (2010) show that areawide suppression of the
European corn borer is associated with Bt corn use. They estimate that the
cumulative benefits of Bt adoption over 14 years exceed $6 billion for corn
growers in Illinois, Minnesota, Wisconsin, Iowa, and Nebraska. Non-
adopters captured $4.3 billion of these benefits because they reap the
rewards associated with low infestation rates without paying a premium for
insect-resistant seeds.
Carrière et al. (2003) conducted a 10-year study in 15 regions across
Arizona and showed that Bt cotton suppressed a major pest, the pink
bollworm, “independent of demographic effects of weather and variation
among regions.” Pink bollworm population density declined only in
regions where Bt cotton was abundant. Such long-term suppression has not
been observed with insecticide sprays, suggesting that deployment of Bt
crops may also contribute to reducing the need for insecticide sprays.
Earlier, Marra et al. (2002a) considered the side-by-side trials of Bt
and conventional varieties. They discuss the bias caused by the “halo
effect” that arises from the insect suppression of the Bt crops spilling over
onto the conventional treatments, thus increasing the yield of the
conventional crop relative to what it would be if the conventional crop
were grown in isolation. This effect biases downward the yield difference
between the Bt and conventional varieties.
