Fallow land sown with a wildflower seed mixture is one of the major set-aside areas promoted by the Swiss legislation in order to enhance biodiversity in the landscape. Still, the installation of such areas on arable land raises concerns about their potential to contribute to the dissemination of noxious weeds. In order to gather information about weed development in such fallows, botanical observations have been carried out, between 2003 und 2005, on about 200 of them nationwide. The majority presents an intresting or even excellent botanical composition. Nevertheless, several weeds were regularly observed, especially creeping thistle, broad-leaved dock, couch grass and bindweed. We estimate that about 5-10 % of the fallows present a critical weed situation – mainly because of thistels. Moreover, Solidago species (S. Canadensis, and S. gigantnea) are present in about a third of them. Control methods are now under development to reduce the impact of these invasive species.
Noxious weeds in set-aside areas: results of a nationwide observation network