Oct 27, 2003

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British study on herbicide strategies and biodiversity

“Taking a more differentiated view”

It is even being debated in the Bundestag: the British study on the possible effect of herbicide management strategies in maize, rape and beet cultivation on species diversity has also caused a stir in Germany. Opponents of genetic engineering feel vindicated; experts, who have been looking at farmland biodiversity for some time, warn against drawing sweeping conclusions. - GMO Safety spoke to Dr. Bernd Hommel from the BBA (Federal Biological Research Centre for Agriculture and Forestry) in Kleinmachnow.

GMO Safety: What is your initial impression of the British study?

Bernd Hommel: I think the study is highly significant for Germany too, because it adopts a very comprehensive and realistic experimental approach. The trials included a broad range of management practices, providing a realistic background to compare different methods of weed management.

GMO Safety: At the Federal Biological Research Centre in Dahnsdorf you have been working on similar problems for quite some time now. You have also conducted trials in this field. Would you expect similar findings for Germany as for Britain?

Bernd Hommel: We have been gathering experience of herbicide-tolerant maize and rape since 1996. With these crops we expect the results for German agriculture to be similar. However, with sugar beet we expect somewhat lesser differences between conventional methods of weed management and the new HT regime. But in terms of biodiversity and abundance we should not regard the assessment of the new HT regimes with GM plants as final. Our British colleagues compared the new strategy with conventional management practices over a three-year period. But this can never be anything other than a snapshot. If greater biodiversity and plant density were found in the associate field flora in conventional summer rape and beet fields, then in agronomic terms this often reflects the gaps in the spectrum associated with conventional weed control methods. But the aim of developing new active ingredients and the common practice of combining several active ingredients was and still is to minimise these gaps wherever possible. The new HT technology could be used to counter this. The British results for maize certainly point to that.

GMO Safety: In farming language, rich farmland biodiversity can also be expressed more simply as a high incidence of residual weeds. These are plants that compete with the crops and, in the absence of control, lead to high yield losses particularly in crops planted in rows, such as sugar beet and maize. So surely it cannot be the farmer’s objective to maximise biodiversity on his land? Or should we be taking a more differentiated view?

Bernd Hommel: In this case we must assume there are competing objectives. In agronomic terms it should be noted that biodiversity and abundance, as measured in the study, are tolerated by farmers, provided that they do not represent a financial risk, in other words provided they do not lead to a reduced yield or loss of quality. On the other hand, farmers are actually interested in a certain amount of residual weed growth, because they can use it to protect the soil from erosion and make savings through less intensive weed control.

GMO Safety: Do you think these relationships should have received greater emphasis in the British study?

Bernd Hommel: In my view further evaluations should focus on these very aspects. For example we should question whether practices which result in increased biodiversity and more plants on the fields (i.e. residual weed infestation) cause problems in the following crops. Such a situation currently exists today in our rape fields, where weed species related to rape have been selected over several years. There are problem weeds hiding in the associate field flora as well, which then have to be controlled with increased use of herbicides or new active ingredients when they multiply rapidly in the following crop. Here too a much more differentiated approach is needed. But the three-year British study was not long enough for this.

GMO Safety: The findings of this study can also be seen as a key contribution to the discussion on more environmentally friendly weed management systems, can’t they?

Bernd Hommel: Absolutely – with its broad database the British study has for the first time provided comprehensive material on conventional herbicide practices. It gives statistically reliable information relating to the number of conventional active ingredients used, the dosage and the number of applications. On this basis, conventional practices can be assessed as equivalent to herbicide-tolerant practices and even inferior in the case of sugar beet. The reduction by one third in the number and quantity of active substances applied and the halving of spraying applications in HT sugar beet are not only of economic interest to the farmers – they also contribute to environmental sustainability, particularly to maintaining the fertility of the soil. When evaluating agronomic practices, biodiversity is not the only criteria to be considered in the field in question.

GMO Safety: Thank you very much