‘Flavescence dorée’ (FD) is a quarantine grapevine disease associated with FD phytoplasmas (FDp). In Switzerland, FD was first reported in 2004 in the southern part of the Canton Ticino, from where, within a few years, it spread to nearly the entire vineyard area of the Southern Alps, despite the mandatory control measures. The aim of this study was to assess the possible role of gone-wild grapevines (GWGVs) in forests resulting from early abandoned vineyards as a habitat for the main FDp vector, Scaphoideus titanus, and for the best alternative vector candidate, Orientus ishidae, as well as an FDp inoculum reservoir in Southern Switzerland. Leaf samples were collected in 20 plots and tested for the presence of FDp. Moreover, fifteen of these plots were monitored with yellow sticky traps to determine the presence and infection status of insect vectors. Finally, a hatching experiment under controlled conditions was conducted to investigate the possible oviposition activity by FDp vectors, using wood collected from GWGVs present in 11 forest sites in the surroundings of cultivated vineyards. GWGVs in forests were confirmed to act as an FDp reservoir and to represent a suitable habitat for FDp vectors (in particular, for S. titanus). Abandoned vineyards should be included in the FD management strategy and their systematic rogueing should be applied as soon as possible and in particular before the transition from vineyard to forest occurs, in order to avoid the survival of S. titanus and the establishment of inoculum in uncontrolled landscape compartments.