Flavescence dorée (FD) is a detrimental grapevine’s disease associated with the quarantine organism ‘Candidatus Phytoplasma vitis’ (FDp), which leads to important economic losses to European viticulture. FDp is acquired and transmitted by the leafhopper Scaphoideus titanus, which is responsible for the rapid spread of the disease. No curative methods are currently available and so far, control measures have been targeted at the vineyard scale, disregarding the role of landscape as a possible source of inoculum and as a suitable habitat for the vector population. In addition to abandoned vineyards and gone-wild grapevines, which may represent an important FDp and S. titanus reservoir and habitat, several alternative vectors and host plant species have been identified in the landscape as possible actors in the FD epidemics. In the specific case of Southern Switzerland, the East Palearctic leafhopper Orientus ishidae along with the plant species Alnus glutinosa have been described as functioning actors in the maintenance of FDp in the landscape. O. ishidae is a polyphagous insect and widely found on plant species such as Corylus avellana, Acer spp., Salix spp, and even on Vitis spp., on which it is also able to oviposit. The role that such alternative FDp epidemiological cycles may play is not negligible, considering that 28.1% of the vineyard perimeter directly borders the forest at less than 10 m due to the specific geomorphology and cultural practices of Southern Switzerland. This is additionally aggravated by the fact that previous works found up to 85% of O. ishidae specimens sampled from alder infected by FDp genotypes compatible with both S. titanus and grapevine and other FDp-like phytoplasmas, while 100% of the tested alders resulted infected. C. avellana, which is a typical forest edge species in Southern Switzerland and a highly suitable host of O. ishidae, may act as a bridge between alder stands and vineyards. In the frame of this study, during winter 2021/22, a habitat management experiment was conducted in order to test the impact of selective removal of hazelnuts for the control of O. ishidae. Based on the monitoring activities of 2021, the trap positions representing O. ishidae capture hotspots were selected for the experiment. During the dormant period, all existing hazelnuts within a radius of 3 m from the trap position were coppiced and the resulting woody material was quantified (diameter and length) and removed from the experimental plots. The effect of habitat management on the O. ishidae population was assessed by placing the traps in the same locations from June 2022 until October 2022. In the treated sites, the O. ishidae mean populations showed a marked decreasing trend, which went far beyond the seasonal reduction observed on the control traps installed in untreated sites, confirming the positive impact of the selective removal of hazelnuts. Habitat management may thus serve as an integrative tool to lower the risk of FDp flow between the forest and the cultivated compartments by lowering the population of the alternative vector O. ishidae.
