GM Crops: The First Ten Years - International Service for the ...

GM Crops: The First Ten Years
Table 39. Average US maize herbicide usage and environmental load: GM HT and
conventional cotton in the US 1997-2005
Year Average ai/ha kg: Average ai use (kg/
conventional cotton ha): GM HT cotton
1997
1998
1999
2000
2001
2002
2003
2004
2005
2.1
2.27
1.92
2.11
1.93
1.87
1.65
1.63
1.60
2.38
2.52
2.27
2.34
2.51
2.50
2.53
2.71
2.79
Average field EIQ/ha
conventional cotton
Sources and notes: derived from Doane 1998-2005. 1997 based on the average of the years 1997-1999
48
52
44
49
45
43
37
36
36
Average field EIQ/ha:
GM HT cotton
The reader should, however note that this comparison between the GM HT crop and the conventional
alternative is not a representative comparison of the average GM HT crop with the average
conventional alternative and probably understates the herbicide usage for an average conventional
cotton grower, especially as the level of GM HT cotton usage has increased. This is because the
first users of the technology were those with greatest levels of weed problems and more intensive
producers, with average to above average levels of herbicide use. Also, once uptake of the
technology began to account for a significant part of the total US cotton area (from 1999 when the
GM HT share became over 40% of the total crop), the residual conventional cotton growers have
been those in locations with lower than average weed infestation levels and/or regions with a
tradition of growing cotton on an extensive basis (and hence have historically used below average
levels of inputs such as herbicides, eg, West Texas). As such, the average herbicide ai/ha and EIQ/
ha values recorded for all remaining conventional cotton growers tends to fall and be lower than
the average would have been if all growers had still been using conventional technology. One
way of addressing this deficiency is to make comparisons between a typical herbicide treatment
regime for GM HT and a typical herbicide treatment regime for an average conventional cotton
grower that would deliver a similar level of weed control to that level delivered in the GM HT
system in the same location.
This is the methodology used by the NCFAP (2003 and 2005). Based on this approach the respective
values are, for conventional cotton, average herbicide ai use 5.67 kg/ha and a field EIQ/ha of 130/
ha, and for GM GT cotton, herbicide ai use 3.72 kg/ha and a field EIQ of 63.8/ha. Given that these
values are significantly higher than the average values for use across the US cotton in any year, we
have therefore adjusted these values downwards to reflect actual average usage levels. On this
basis the comparison level of usage recorded (and used in the national level analysis below) is:
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• conventional cotton average, herbicide ai use 3.5 kg/ha and a field EIQ/ha of 95.6/ha;
• GM GT cotton, herbicide ai use 2.29 kg/ha and a field EIQ of 46.9/ha.
46
51
43
44
47
46
46
49
48