Jun. 6, 2016
Since 1996, the use of pesticides on the GM crop area was reduced by 581.4 million kg of active ingredient (8.2% reduction), and the environmental impact associated with herbicide and insecticide use on these crops, as measured by the Environmental Impact Quotient (EIQ) indicator, fell by 18.5%, according to the report published by P G Economics. 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 (Table 1).
Note: 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 production, the author assumed that the conventional alternative delivers the same level of weed control as occurs in the GM HT production system.
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 43% reduction in the total volume of active ingredient used on GM crops (-249.1 million kg active ingredient, equivalent to a 27.9% reduction in insecticide use on the GM IR cotton area) and a 36% reduction in the total field EIQ indicator measure associated with GM crop use (1996-2014) 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 (79.7 million kg of active ingredient), with associated environmental benefits.
The volume of herbicides used in GM maize crops also decreased by 213.7 million kg (1996-2014), an 8.4% reduction, whilst the overall environmental impact associated with herbicide use on these crops decreased by a significantly larger 12.6%. 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, whilst herbicide use increased by 5.5 million kg (1996-2014), the associated environmental impact of herbicide use on this crop area decreased (improved) by 14.1%, due to a switch to more environmentally benign herbicides. In the canola sector, farmers reduced herbicide use by 21.8 million kg (a 17.2% reduction) and the associated environmental impact of herbicide use on this crop area fell by 29.3% (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 2 shows a 53%:47% split of the environmental benefits (1996-2014) respectively in developed (53%) and developing countries (47%). Seventy per cent of the environmental gains in developing countries have been from the use of GM IR cotton.
It should, however, be noted that in some regions where GM HT crops have been widely grown, some farmers have relied too much on the use of single herbicides like glyphosate
to manage weeds in GM HT crops and this has contributed to the development of weed resistance. There are currently 35 weeds recognised as exhibiting resistance to glyphosate worldwide, of which several are not associated with glyphosate tolerant crops. For example, there are currently 15 weeds recognised in the US as exhibiting resistance to glyphosate, of which two are not associated with glyphosate tolerant crops. In the US, the affected area is currently within a range of 30%-50% of the total area annually devoted to maize, cotton, canola, soybeans and sugar beet (the crops in which GM HT technology is used).
In recent years, there has also been a growing consensus among weed scientists of a need for changes in the weed management programmes in GM HT crops, because of the evolution of these weeds towards populations that are resistant to glyphosate. Growers of GM HT crops are increasingly being advised to be more proactive and include other herbicides (with different and complementary modes of action) in combination with glyphosate in their integrated weed management systems, even where instances of weed resistance to glyphosate have not been found.
This proactive, diversified approach to weed management is the principal strategy for avoiding the emergence of herbicide resistant weeds in GM HT crops. It is also the main way of tackling weed resistance in conventional crops. A proactive weed management programme also generally requires less herbicide, has a better environmental profile and is more economical than a reactive weed management programme.
At the macro level, the adoption of both reactive and proactive weed management programmes in GM HT crops has influenced the mix, total amount and overall environmental profile of herbicides applied to GM HT soybeans, cotton, maize and canola in the last 7-10 years.