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Differing studies
Cultivation of genetically modified plants: more or less pesticide?
(17.11.2009) Two current studies on the environmental
influence of genetically modified (GM) plants arrive at differing results.
According to one study, significantly more pesticide has been applied to fields
since the cultivation of genetically modified plants began in 1996. The other
study books substantial environmental relief through GM plants.
One study, authored by Charles Benbrook and published by
the American non-governmental organisations The Organic Center and Union of
Concerned Scientists, has come to a negative result: since the market entry of
herbicide-resistant GM plants in the USA in 1996, the quantity of applied
 herbicide
has increased by 175 million kilogrammes, of which 46 per cent fall in the years
2007 and 2008 alone. According to Benbrook, primarily in the south of the USA
numerous weeds have spread in the meanwhile that have developed resistance to
the herbicide agent glyphosate (Roundup) suited to the GM plants. Many
farmers attempt to combat these weeds through higher doses of glyphosate or
through the application of other herbicide agents. For this reason, a further
increase in the amount of deployed pesticide may be expected.
In contrast, a positive balance is found in the study
conducted by the British agricultural economist Graham Brookes (PG Economics).
He ascertained a world-wide decrease in the application of herbicide between
1996 and 2007 due to the cultivation of GM plants. According to the study,
approximately 200 million fewer kilogrammes of herbicide were deployed. However,
in contrast to Benbrook, Brookes did not compare the total quantity of herbicide
deployed but the quantities of active agent. In the case of soy, according to
Brooks, a reduction in deployed herbicide agent of 4.6 per cent in comparison to
the level of 1996 was found as a result of the cultivation of
herbicide-resistant varieties. In the case of cotton, this figure was 15 per
cent.
With regard to insect-resistant plants, the studies
arrive at similar conclusions: Benbrook determined a reduction in the
application of plant protection agents by 28 million kilogrammes since 1996 as a
result of the cultivation of Bt maize and Bt cotton.
According to Brookes, the worldwide application sank by
as much as 157 million kilogrammes. Once again, this was stated in terms of the
active agent. For this study, primarily cotton contributed to environmental
relief through insecticide reduction. However, neither China nor India, which
have large field areas of Bt cotton, were addressed by Benbrook.
In total, Brookes calculates a global environmental
relief of 17 per cent due to the lowered need for insecticide and herbicide in
the cultivation of GM plants. In contrast, Charles Benbrook states the stark
increase in glyphosate-resistant weeds as the primary problem. As a result, he
expects rising costs, declining yields and increasing environmental strain.
See also on GMO Compass:
Further information:
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