Noxious weeds in set-aside areas: results of a nationwide network in Switzerland
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. About 200 fallow lands have been monitored for 3 years (2003-2005) during summers in different Swiss areas, in order to list the main weeds and estimate their abundance.
Weeds
Cirsium arvense (Asteraceae), Rumex obtusifolius (Polygonaceae), Elytrigia repens (Poaceae), Convolvulus arvensis (Convolvulaceae) are respectively the most represented weeds in the monitored fallows. About 5 to 10% of the fallows were estimated to present a critical weed situation.
While infestations remain limited, some difficult cases have justified the registration of several herbicides on fallow lands, such as glyphosate which is a non selective herbicide, or other selective herbicides like metsulfuron against Rumex obtusifolius, clopyralid against Cirsium arvense, or graminicides against Elytrigia repens.
Invasive alien plants
Ambrosia artemisiifolia (Asteraceae) has never been found in the survey, but other neophytes have been observed sporadically: Buddleia davidii (Buddleiaceae, EPPO List of IAP), Oenothera biennis (Onagraceae), Reynoutria japonica (Polygonaceae, EPPO List of IAP), Senecio inaequidens (Asteraceae, EPPO List of IAP). Solidago canadensis and S. gigantea (Asteraceae, EPPO List of IAP) appear to be the biggest problem, since about one third of fallow lands sown with wildflower seed mixtures are covered (up to 50% of the surface area) by these species. Solidago spp. are not considered a threat to agriculture, but to indigenous flora and biodiversity. Fallow lands aimed at promoting biodiversity in agricultural areas are paradoxically helping the establishment and spread of an invasive alien plant.
As conclusion, while the situation of weeds in fallow lands in Switzerland is globally considered as satisfactory, invasion by Solidago spp. constitutes a particular problem. The possible registration of herbicides to control specifically Solidago spp. or other invasive alien species (such as Reynoutria japonica) in fallow lands may be considered.
Sources
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Delabays N, Mermillod G, Bohren C (2007) Plantes indésirables dans les jachères florales: résultat d’un réseau national d’observation. Revue Suisse d’Agriculture, 39(4): 199-203.
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