GMOs and Pesticide Use: Systematic Reviews

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GM CROPS: GLOBAL SOCIO-ECONOMIC AND ENVIRONMENTAL IMPACTS 1996- 2013 (2015) Brookes and Barfoot PG Economics

Environmental impact from changes in insecticide and herbicide use
To examine this impact, the study has analysed both active ingredient use and utilised the indicator known as the Environmental Impact Quotient (EIQ) to assess the broader impact on the environment (plus impact on animal and human health). The EIQ distils the various environmental and health impacts of individual pesticides in different GM and conventional production systems into a single ‘field value per hectare’ and draws on key toxicity and environmental exposure data related to individual products. It therefore provides a better measure to contrast and compare the impact of various pesticides on the environment and human health than weight of active ingredient alone.
Readers should, however, note that the EIQ is an indicator only (primarily of toxicity) and does not take into account all environmental issues and impacts. In the analysis of GM HT technology we have assumed that the conventional alternative delivers the same level of weed control as occurs in the GM HT production system.
GM traits have contributed to a significant reduction in the environmental impact associated with insecticide and herbicide use on the areas devoted to GM crops. Since 1996, the use of pesticides on the GM crop area was reduced by 550 million kg of active ingredient (8.6% reduction), and the environmental impact associated with herbicide and insecticide use on these crops, as measured by the EIQ indicator, fell by19%.
In absolute terms, the largest environmental gain has been associated with the adoption of GM insect resistant (IR) technology. GM IR cotton has contributed a 26.6% reduction in the volume of active ingredient used and a 29.4% reduction in the EIQ indicator (1996-2013) due to the significant reduction in insecticide use that the technology has facilitated, in what has traditionally been an intensive user of insecticides. Similarly, the use of GM IR technology in maize has led to important reductions in insecticide use (71.7 million kg of active ingredient), with associated environmental benefits.
The volume of herbicides used in GM maize crops also decreased by 210 million kg (1996-2013), a 9.2% reduction, whilst the overall environmental impact associated with herbicide use on these crops decreased by a significantly larger 13.5%. This highlights the switch in herbicides used with most GM herbicide tolerant (HT) crops to active ingredients with a more environmentally benign profile than the ones generally used on conventional crops.
Important environmental gains have also arisen in the soybean and canola sectors. In the soybean sector, herbicide use decreased by 2.3 million kg (1996-2013) and the associated environmental impact of herbicide use on this crop area decreased, due to a switch to more environmentally benign herbicides (-14.5%). In the canola sector, farmers reduced herbicide use by 18.4 million kg (a 16.5% reduction) and the associated environmental impact of herbicide use on this crop area fell by 27.9% (due to a switch to more environmentally benign herbicides).
In terms of the division of the environmental benefits associated with less insecticide and herbicide use for farmers in developed countries relative to farmers in developing countries, Table 7 shows a 54%:46% split of the environmental benefits (1996-2013) respectively in developed (54%) and developing countries (46%). About three-quarters (72%) of the environmental gains in developing countries have been from the use of GM IR cotton.



On average, GM technology adoption has reduced chemical pesticide use by 37%, increased crop yields by 22%, and increased farmer profits by 68%. Yield gains and pesticide reductions are larger for insect-resistant crops than for herbicide-tolerant crops. Yield and profit gains are higher in developing countries than in developed countries.


SOUTH AFRICA – BT COTTON: Bt growers applied lower amounts of pesticides and had lower biocide indexes than growers of non-Bt cotton.
Hofs, Fok, and Vaissayre (2006) observed a decrease in pyrethroid use during the 2002/03 and 2003/04 seasons, though farmers did not abandon the pesticide. At the same time, farmers applied substantial amounts of organophosphates to control pests not affected by the Bt toxin.
After quantities of insecticide applied by farmers were converted into a biocide index and an environmental impact quotient (EIQ), to allow for differences in toxicity and persistence in the environment, Morse, Bennett, and Ismael (2006) found evidence of environmental benefits associated with growing Bt cotton, for all three seasons of study and for both bollworm and non-bollworm categories of insecticide.
CHINA – BT COTTON: The first year of survey data in China (1999) included 282 farmers in Hebei and Shandong provinces. Yields did not differ significantly between Bt and non-Bt growers, but non-Bt growers used five times as much pesticide and paid seven times as much for it.
Bt use reduced the utilization of pesticides, particularly organophosphates. Farmers benefited most from savings in pesticide expenditures and labor, since at that time the yields of major Bt and non-Bt varieties were statistically “indistinguishable”.
INDIA – BT COTTON: Barwale et al. (2004) reported an average 30 percent yield advantage for Bt hybrids compared to non-Bt hybrids, higher net profits, lower application rates for pesticides, and better cotton quality.
Bennett, Ismael, and Morse (2005) showed that official Bt varieties significantly outperform the unofficial varieties, but that unofficial, locally produced Bt hybrids can also perform better than non-Bt hybrids. They reported that second generation Bt seed appears to have no yield advantage over non-Bt hybrids but can save on insecticide use.
MEXICO AND ARGENTINA – BT COTTON: Authors compared estimated parameters across larger and smaller farms and, within adopting farms, between Bt and non-Bt plots. By evaluating conditions on Bt and non-Bt plots operated by the same farmer, selection and placement bias are effectively controlled. The authors found that large family businesses benefited from Bt cotton primarily through reduced pesticide use, since pesticide use is correlated with farm size
ARGENTINA – RR SOYBEANS: While herbicide applications in RR cultivation were higher, herbicide costs per hectare were significantly lower for RR as compared to conventional soybeans. Similar to experiences in the United States, they found that while glyphosate applications had increased, the number of applications from other herbicide families had decreased. One of the main reasons for higher glyphosate applications was the increase in no-till farming practices in Argentina.
SOUTH AFRICA – BT MAIZE: Using only farm survey analyses, they find that yields are higher for both groups and pesticide applications are reduced, particularly for large commercial farmers.