Agroscope, Institute for Plant Production Sciences IPS, 1260 Nyon, Switzerland

New problem plants and weeds in Switzerland – a threat to agriculture and natural areas?

The increasing number of naturalized nonnative (exotic) plant species is a significant component of global change in most regions of the world. In agricultural areas new exotics may cause new weed problems and may demand for new control measures. In natural areas newly established exotic species may become dominant and suppress native vegetation, thus threatening native biodiversity. Changes in land use and agricultural practice make the appearance of new weeds likely. In order to prevent future weed problems on agricultural land and future plant invasions in natural areas, the introduction and spread of new weeds should be avoided. This requires methods for recognizing potentially new weeds and appropriate control measures of species that are already established. The potential for new weeds is high in Switzerland. A survey of the most troublesome weeds in European countries has shown that several countries contain species that are not yet present or do not yet cause major problems in Switzerland but might become invasive under favourable conditions in the future. Species most likely to cause new weed problems in Switzerland include Indian mallow (Abutilon theophrasti), common marshelder (Iva xanthi folia), and paradoxagrass (Phalaris paradoxa). Newly established species in natural areas and disturbed sites include biennial wormwood (Artemisia biennis), devils beggarticks (Bidens frondosa), and American willowherb (Epilobium adenocaulon). These species are serious problem plants in other regions.

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