Hope Not Hype - Third World Network

Yield
57
sistance-management schemes even though to date management has been successful
(Heinemann, 2007; Tabashnik et al., 2008).
The above discussion notwithstanding, some studies have found yield improvements
in some crops, at some times and in some locations, and others have found no yield increases
or actual declines. For example, contrast the following two results for GM insecticide
cotton in India:
vs.
Average yields of Bt [cotton] hybrids exceeded those of non-Bt counterparts and popular
checks by 80% and 87%, respectively (p. 900)…Over the 4-year period from 1998 to 2001,
Bt hybrids showed an average advantage of 60% (Qaim and Zilberman, 2003, p. 901).
The cultivation of the genetically modified bollworm-resistant Bt cotton was recently
authorised in India. Although increased yields and profits, along with reduced pesticide applications
have been credited to its introduction, also many cases of poor performance have
been reported, particularly in Andhra Pradesh (Mancini et al., 2008, p. 23).
A general weakness of collecting anecdotes of either yield increases or decreases is
the potential variability in varieties being compared, locations, particular seasons and other
parameters. However, the question here is whether confidence is justified in the general
claim that GM plants increase yield and will do so under real world conditions that include
environmental variables and the ways in which they are being developed and distributed
by industry. The anecdotes reveal that confidence is not justified in such general claims.
The same kind of yield variability is seen with cotton in other parts of the world. For
GM insect-resistant cotton, average yield increases were 33% in Argentina, 19% in China,
34% in India, 11% in Mexico and 65% in South Africa. However, the authors note that
“the averages conceal a high degree of temporal and spatial variation” even though “they
clearly indicate positive overall results” (Raney, 2006, Table 1 and p. 175). Considering
both HT and insecticide cotton varieties in the US, the latest studies do not vindicate the
claim that testing has been exhaustive and that the crops are reliably increasing yield or
financial returns.
Field experiments were conducted to compare production systems utilizing cotton cultivars
possessing different transgenic technologies managed in accordance with their respective
genetic capabilities. In 2001 and 2002, selection of the Roundup Ready (RR) technology
system resulted in reduced returns to the producer, while higher returns were attained from
nontransgenic, [insecticide-producing] Bollgard (B), and Bollgard/Roundup Ready (BR) technologies.
[“This outcome is consistent with the reduced yields observed with the RR cultivars”
(p. 48).] In 2003, selection of the RR technology system or the Bollgard II/Roundup
Ready (B2R) system reduced returns, while similar, higher returns were attained from
nontransgenic, B, and BR technologies. [“Again, lint yields generally followed returns” (p.
48).] In 2004, a nontransgenic system was superior to the BR, B2R, and Liberty Link (LL)
systems in Tifton, but similar returns were achieved from nontransgenic, BR, and B2R tech-