Amaranthus palmeri S. Watson. A new threat to agriculture in Europe and the Mediterranean region

Amaranthus palmeri S. Watson is a dioecious broad-leaved species characterised by rapid growth, high seed production, efficient resource use and adaptability to diverse environments and cropping systems. A. palmeri populations are spreading beyond their native range in south western United States, into the Mediterranean region and have been reported in several European and Mediterranean countries. First stands were located along roadsides, and later in nearby agricultural fields. Possible routes of introduction include contaminated animal feed and grain shipments for industrial processing. Some European A. palmeri populations appear to be already resistant to 5-enolpyruvylshikimate-3-phosphate synthase and acetolactate synthase inhibitors when imported. Recent studies suggest that this trait may have evolved in the origin country before the introduction into southern Europe and the wider Mediterranean region. Effective, transboundary networks have to be established between farmers and researchers to raise agricultural community awareness and continuously monitor the invasiveness of A. palmeri in Europe. In this review, we first highlight botanical characteristics that allow accurate identification of A. palmeri from closely related Amaranthus species. Then, we summarise recent reports on the occurrence of A. palmeri in Europe and the Mediterranean region. We proceed to assess future invasion and spread across Europe according to climate and agricultural practices. In addition, we review measures to early detect A. palmeri and emphasised on feasible, chemical and non-chemical weed control methods as components of integrated weed management to mitigate the impact of A. palmeri invasion on European agriculture.