Border effect in spatial distribution of Flavescence dorée affected grapevines and outside source of Scaphoideus titanus vectors.

Flavescence doree (FD) is a severe Grape Yellows Disease of European vineyards whose phytoplasma causal agent is transmitted from grapevine to grapevine by the leafhopper Scaphoideus titanus Ball. Grapevines untreated with insecticides are considered potential sources of infectious vectors for treated vineyards. Research was carried out: (i) to study the spatial distribution of grapevines affected by FD, (ii) to compare the S. titanus population levels between treated and untreated vineyards and (iii) to verify if there are decreasing gradients of S. titanus adult captures in treated vineyards from contiguous untreated grapevines. In two vineyards with potential external sources of infected S. titanus populations in the near vicinity, a significant decreasing gradient of grapevines affected by FD was observed. In two other vineyards without untreated grapevines potential sources of infectious S. titanus in surrounding areas, an edge effect was not observed. The vineyards untreated with insecticides, both cultivated and abandoned, showed much higher population levels of S. titanus than treated vineyards. In vineyards treated against the vector, a decreasing gradient of S. titanus adult captures was observed from contiguous untreated grapevines. This occurrence shows that the vector moves from untreated grapevines to treated vineyards. So, if adult vectors moving from untreated grapevines are infected by FD phytoplasmas, they can represent a real risk for the surrounding vineyards treated with insecticides. Therefore, the strategy for effective FD control needs to also include: (i) insecticide treatments effective against S. titanus in all the grapegrowing areas with vineyards affected by FD and (ii) the eradication of abandoned vineyards and American grapevines growing wild in spontaneous vegetation.