Perspectives for biological control

The recent invasion by common ragweed, Ambrosia artemisiifolia, has, like no other plant, raised the awareness of invasive plants in Europe. Recently, chemical and mechanical control methods have been developed and partially implemented in Europe, but sustainable control strategies to mitigate its spread into extensively managed land and to reduce its abundance in badly infested areas are lacking. One management tool not yet implemented in Europe but successfully applied in Australia is biological control. With the notable exception of the recently detected leaf beetle Ophraella communa, almost all natural enemies that have colonized A. artemisiifolia in Europe are polyphagous and impose only little damage, rendering them unsuitable for a system management approach. Two fungal pathogens have been reported to adversely impact A. artemisiifolia in the introduced range, but their biology makes them difficult for mass production and application as a mycoherbicide. In the native range of A. artemisiifolia, on the other hand, a number of herbivores and pathogens associated with this plant have a very narrow host-range and reduce pollen and seed production, the stage most sensitive for long-term population management of this winter annual. We discuss and propose a prioritisation of these biological control candidates for a classical or inundative biological control approach against common ragweed in Europe by considering past experiences from North America, Asia and Australia. We argue that the biological control approach should be considered as an integral part of an integrated management approach against common ragweed in Europe. Along these lines, the COST action ‘SMARTER’ (launched in 2012) aims at promoting biological control against common ragweed, integrating it with available chemical and physical control options, and developing habitatand region-specific recommendations for a integrated management of common ragweed across Europe.