Factors affecting the spread of Bois Noir disease in Italian ‘Lambrusco’ vineyards.

During 2003-2006 a research was carried out in 17 vineyards cv. Lambrusco to assess the influence on “bois noir” disease (BN) spreading of the insecticides applied on grapevine canopies and of the environment surrounding vineyards. The tuf-type I BN phytoplasma, that is associated to nettle, was clearly prevalent in the sampled vineyards. The insecticide treatments did not significantly influence either the density of the vector inside the vineyard, or BN disease spreading. The frequency distribution of symptomatic grapevines in some cases fitted to the Poisson distribution and in others to negative binomial distirbution. In the vineyards with an aggregate distribution of symptomatic grapevines, an edge effect from a border side with nettle was usually observed. The incidence of border sides not contiguous to grapevine rows on vineyard surface results associated to higher levels of BN. The border side with nettle was significantly favourable to disease in the vineyards with aggregate distribution of symptomatic grapevines. All the data support the importance of surrounding vegetation as source of inoculum of the BN phytoplasma.