Is the Removal of Nettles along Ditches Effective in Controlling Bois Noir in Vineyards?

Bois noir (BN) is a grapevine yellows disease associated with ‘Candidatus Phytoplasma (Ca. P.) solani’ that is transmitted to grapevines by the planthopper Hyalesthes obsoletus Signoret which uses herbaceous plants such as Urtica dioica as a pathogen reservoir. Urtica dioica is often widespread along ditches bordering vineyards, and a gradient in decreasing BN symptomatic grapevines is observed from the vineyard edges facing these ditches. In two vineyards in north-eastern Italy, over eight or seven years, the ditch bordering one edge of each vineyard was divided into two sections; in one of these, U. dioica was chemically weeded in April, while the other one remained untreated. The impact of chemical weeding on the spatial distribution of both H. obsoletus captures and newly BN symptomatic grapevines was assessed. The reduction in H. obsoletus captures in the vineyard sector facing the section of the ditch subjected to weeding corresponded to a decrease in newly symptomatic grapevines. These findings demonstrated that nettle removal from areas surrounding vineyards can effectively control BN.