Farm Scale Evaluation: Herbicide-resistant plants and agro-biodiversity

Efficient weed control leads to decline in biodiversity

The cultivation of genetically modified plants comes at the expense of biodiversity in fields. The results of the latest long-term British study are continually being referred to in public debate and are also discussed among scientists. However, the scientific assessment is less clear-cut.

Number of bees (top) and butterflies (above) per plant per year for beet, maize and spring rape (conventional farming, GM herbicide tolerant).Source: Dewar presentation)

The findings of the agro-biodiversity research were presented again at the congress of the British Crop Protection Council (BCPC) which took place from 10 to 12 November 2003 in Glasgow.

During the Farm Scale Evaluation (FSE) programme 250 fields were monitored and evaluated over three years. The idea was to compare conventional weed-control concepts with herbicide-resistant (HR) systems based on GM crops and the complementary herbicide in terms of plant and animal diversity in the fields and field margins.

Alan M. Dewar presented the main results of the FSE in Glasgow. He reemphasised the point that the research looked only at the impacts of different weed management systems on species diversity in the agro-ecosystems, but not the frequency and range of outcrossing, or issues of health safety of products based on GM plants (see presentation).

Dewar summarised the results of the FSE as follows:

  • Less herbicide was used on the fields with the HR system for spring rape, beet and maize than on equivalent fields with conventional weed management systems.
  • With oilseed rape and beet the HR systems lead to fewer weeds and to lower biomass and seed production than conventional herbicide use. The reverse is true for maize.
  • These differences stem from the efficiency of the different weed control systems, not from the genetic modification of the plants in the HR system.
  • For ground beetles, rove beetles, spiders, springtails and snails no effects caused by the various weed control concepts were identified.
  • HR rape and beet fields had fewer butterflies than the conventional fields, while the HR beet fields also had fewer bees. The differences between crop species are, however, much greater.

Bernd Hommel and Bernhard Pallut of the BBA’s Institute for Integrated Plant Protection in Kleinmachnow also presented their trials with HR maize and HR rape at the Glasgow congress. They too had looked at the impacts of these concepts on biodiversity. Their conclusion was that “conservation tillage systems with herbicide-resistant crops have a greater potential in promoting integrated pest management than the same systems that do not use transgenic herbicide-resistant varieties.” (See original article).