GM crops and equivocal environmental benefits

The UK and other European governments have domestic and international statutory obligations to conserve many farmland species, including a wide range of birds, and cannot do so simply by protecting isolated natural sites. This is because farmland-dependent species are wide-ranging, often spending different parts of the year in different habitats. In contrast to the US, which has a wide range of large wilderness areas, European countries have little wilderness of use to species dependent on farmland ecosystems, and a high proportion of relatively intensively farmed land. If we are serious about conserving viable populations of farmland-dependent organisms, then we need agricultural methods that allow wildlife to survive within our farmed landscape.

Biotechnology could enable even greater agricultural intensification by making agrochemicals more efficient and easier to use. The current generation of genetically modified herbicide-tolerant (GMHT) crops are designed to enable higher levels of weed control, and the few comparative studies available (for example, refs 1,2) appear to confirm this. Not only do GMHT crops make weed control cheaper and more efficient, but they are also likely to prove attractive to farmers who, because of climatic or soil problems on their land, find high levels of weed control difficult to achieve economically. These are the very areas that are currently some of the last refuges of UK farmland biodiversity³. On the basis of our analysis of the available data on the link between herbicide use and declines in farmland insects and birds, we believe that increasing herbicide efficiency by widespread use of GMHT crops on UK farmland will further damage natural biodiversity.

Weed control in GMHT crops is achieved by spraying broad-spectrum herbicides, such as glyphosate and glufosinate, during the peak growing season in May and June, when field margin habitats such as headlands, ditches, and hedgerows are in full leaf. Compared with the conventional use of pre-emergence herbicides and in-crop selective treatments, this increases risks of damage from spray drift, especially for crops at a growth stage that demands nozzles to be set high⁴. This is already an agricultural (and liability) problem in the US, where drift has caused considerable damage to non-GMHT crops growing alongside GM crops sprayed with broad-spectrum herbicides^6,7.

It is claimed that these herbicides are more environmentally benign in terms of direct toxicity to humans and wildlife, and that less herbicide would be used. There is some evidence that broad-spectrum herbicides are directly toxic to small invertebrates⁶, and we contend that the volumes of herbicide used are not related to environmental damage; it is the ecological impact of the type of herbicide and its application methods that should be considered. There is too much confusion in this debate between inputs and impacts.

Until recently, risk assessments for the commercial release of GMHT crops in the UK did not consider the likely “indirect” effects on biodiversity. These risks to biodiversity from the widespread use of GMHT crops cannot yet be fully assessed because the basic ecological data needed to do so have not been gathered. We can find no comparative studies of ecological effects of GMHT crops before 1998 either in Europe, or in the US and Canada, where they have been in widespread use since 1997. The UK government has now put in place a regulatory system that addresses these issues, and it has initiated a series of studies comparing the ecological effects of growing GMHT oilseed rape (canola), fodder maize, and beet. These three-year field-scale trials using split-field methodology will generate data enabling a full assessment of ecological risk, and may also identify any remedial measures that might be possible if these crops are given consent for commercial release. Other field-scale research is being carried out in France and Germany.

The ecological risks from using GMHT crops do not apply only in the European situation. In many tropical and subtropical countries similar situations exist, wherein important biodiversity is dependent on traditional farming techniques. Farmed wetlands, such as the grazing marshes of northern Europe and rice-growing areas of the Middle East, are vital to large populations of overwintering birds that depend on invertebrates living within the wet fields. The use of GMHT crops on these areas woud risk direct toxicity and indirect effects on the invertebrates and plants that support such bird populations. These are serious risks that need to be properly assessed before consent is given for the use of herbidice tolerant crops in such areas.

Attempts have been made to manipulate herbicide tolerant cropping systems to increase biodiversity in the field—for example, work on sugar beet at Brooms Barn in the UK. Initial results suggest that it may be possible, by carefully timing applications, to allow weeds to grow (and perhaps even flower) before removing them from the crop, although delaying herbicide applications may well result in an unacceptable yield penalty, which would deter farmers. The need for the damaging herbicide atrazine in maize and other crops might also be avoided, by applying a broad-spectrum herbicide over the crop followed by undersowing with a forage crop. But there is no regulatory mechanism yet in place to ensure that any potential benefits could be delivered at the farm level. Experience over the past 40 years has shown that farmers will use herbicides to their full potential, reducing weed populations to as low a level as economically possible.

This is an issue not about biotechnology as a technique, but about how we use it in agriculture. A more sustainable approach to weed control in arable crops might be to produce GM crops with greater tolerance to weeds, perhaps by achieving more competitive growth and the production of inhibitors from roots, allowing a proportion of wild plants to survive within the crop and its margins. There is considerable potential in GM insect-resistant crops for minimizing environmental impacts of arable agriculture, although it may be necessary to ensure genetic isolation from sexually compatible native species.

The challenge to biotechnologists is to produce crop varieties that move us away from chemically dependent agriculture, while maintaining yields and sustaining farmland-dependent biodiversity. This is surely the real goal of agricultural sustainability, which should be about sustaining levels of production while simultaneously minimizing the environmental impacts of agriculture. So far, the industry has produced no convincing evidence that GMHT crops will contribute to the latter.