GM crops could reduce need for herbicides

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Source: European Commission, Environment DG

Analysis of large-scale European field trial data reveals that lower quantities of herbicides are applied to crops genetically modified for herbicide-resistance compared with conventionally grown crops. However, the data also suggest that biodiversity may be reduced if genetically modified (GM) crops are grown widely.

Transgenic crops are currently grown in 22 countries across the world, including seven EU member states: Spain, France, the Czech Republic, Portugal, Germany, Slovakia and Romania. However, cultivation of GM crops in the EU represents a small proportion of the more than 100 million hectares grown worldwide.

Cultivation of crops resistant to glyphosate, a commonly used herbicide, is limited in the EU1, though such crops are imported and processed. Only Romania has cultivated glyphosate-resistant (GR) transgenic soybean on a large scale, and this occurred before its inclusion in the EU.

The study looked at a number of weed-management strategies, including the use of glyphosate and GM, for three crops: sugar beet, soybean and oilseed rape. The findings reveal that the weed-sensitive crop, sugar beet, is more easily cultivated as a GM crop than a conventionally grown crop and that less herbicide is applied to the GM variety. Studies in the USA and Canada suggest that herbicide applications are reduced in other crops that have been modified for herbicide resistance, including soybean, maize and oilseed rape.

GM crops may also offer benefits in terms of climate change. A life cycle analysis (LCA) of the herbicide production chain, including transportation and field applications, has revealed that adoption of GR beets could reduce energy use by up to 50 per cent and global warming potential by 19 per cent.

The study cites data derived from assessments using the Environmental Impact Quotient (EIQ)2 which estimates and compares the environmental impacts of pesticide spray programmes. This accounts for potential impacts on farm workers, consumers and the environment. EIQ data suggest that negative environmental impacts caused by herbicides are lower for GR crops. However, the UK's farm scale evaluation (FSE) trials with GR beets suggest that the reduction of weed and insect species could possibly undermine biodiversity and have impacts on species higher up the food chain. This includes birds that are reliant on insects as a food source.

The authors conclude that cultivation of GR crops could provide an alternative method of weed management with positive effects for the environment, as long as measures for maintaining biodiversity are taken. In addition, it would be necessary to prevent herbicide resistant plants becoming 'volunteer' weeds (plants that have not been planted deliberately) in subsequent crop rotations. The cross-pollination of GM varieties with closely related plant species is also a concern. Therefore, if GM crops are to be adopted on a wider scale, changes to wider agricultural practices are needed. For example, the use of other herbicides may be needed to control volunteers.

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