Editorial

Citation

Wells, D. (1999), "Editorial", Nutrition & Food Science, Vol. 99 No. 3. https://doi.org/10.1108/nfs.1999.01799caa.001

Editorial

A scientific review of the impact of herbicide use on genetically modified crops has recently been circulated to interested organisations by the Ministry of Agriculture, Fisheries and Food. It examines the reasons for herbicide use on conventional and GM crops and considers the differences these might bring in terms of the impact on biodiversity and on the timing and extent of the herbicide use.

The genetically modified herbicide-tolerant (GMHT) crops that are the most likely to be introduced in the UK in the foreseeable future are winter and spring oilseed rape, sugar beet, fodder beet and forage maize. These crops have been modified to be tolerant to the herbicides glyphosate and glufosinate-ammonium. These herbicides are active against a wider range of plant species. They are taken up only by the leaves and shoots of weeds that have emerged from the ground at the time of application.

The review covers a wide range of weed problems. For example, the time the crop is sown is a major factor in determining the weed species that are most important. Weeds can cause severe problems in crops resulting in yield losses of around 20 to 60 per cent if they are not controlled. Hence growers aim for and usually achieve high levels of weed control in these crops. To do this they currently employ a range of cultural techniques together with complex mixtures and sequences of several types of herbicide, particularly in sugar beet. Weed control measures begin before the crop emerges with cultivation and the use of herbicides that act against weeds in the soil. After the crop emerges, herbicides are mostly applied against weeds that have only a few leaves as these are better controlled by available herbicides.

In contrast, due to their activity on larger weeds of a range of species, use of glyphosate and glufosinate in GMHT crops offers the user a simpler programme of sprays that can be applied after the crop emerges. Weed control is likely to be achieved using two or three applications of these herbicides with perhaps another herbicide being used for particular problem weeds. This programme is likely to provide equivalent or slightly better control of annual weeds and more effective control of some perennial weeds than currently achieved. There is the opportunity to delay weed control in the GMHT crop by a few weeks when compared with current practice. If weeds become too large then competition with the crop at an early stage of its growth can lead to loss of yield.

Some advisers consider the flexibility of weed control in GMHT crops and the improved control of some important species gives the opportunity to re-examine weed control practice throughout the crop rotation. In GMHT crops different weed control practices could be considered which favour growth of weeds at times of the year and in parts of the fields where they do not compete with the crop. It is possible that more annual broad-leaved weeds could be left in cereals and that different crop establishment practices could also be adopted throughout the rotations with a move to minimal cultivation and to leave more weeds in stubbles.

There is at present little independent research to allow an accurate prediction of the potential impacts on wildlife of the introduction of GMHT crops. A number of scenarios arise from the impact of weed control both on these crops and throughout rotation. Different potential scenarios result in negative and positive impacts on the abundance of weed species and associated biodiversity, or the effects may be comparable to current practice.

Herbicide application to all crops is required to be carried out accurately to prevent impact on hedgerows and field margins. There is currently no evidence that the approved use of herbicides on field crops has had a direct effect on the biodiversity of these areas.

A phased, monitored introduction of GMHT crops into the UK has been proposed. Weed control practices more favourable to biodiversity could be tested during these introductions and environmental effects closely monitored.

Dilys Wells