Mal dell'esca. Stato attuale delle conoscenze

The Esca is a complex disease produced by five different syndromes: dark streaks of young grapevines, Petri disease, white rot, young esca and proper esca. The external manifestations can be white rot, cloro-necrosis of leaves ( the striped leaves), apoplexy (sudden death of plant). The fungi detected in the esca complex are Phaemoniella chlamydospora (Pch), Phaeoacremonium aelophilum (Pal) and Fomitiporia mediterranea (Fmed). Pch and Pal are mainly responsible for dark streaks, Petri disease and young esca, while Fmed is responsible for white rot. The concurrent presence of the three kinds of fungi produce the proper esca. In longitudinal section dark streaks show single or grouped stripes, while in transversal section we see black dots all around the central pith. Generally they are shown in the grafting point. The Petri disease is similar to the previous syndrome but it also shows emission of dark gum when sectioning, while leaves present moderate chlorosis. The young esca may be the evolution of previous disease (dark stripes and typical striped leaves). The white rot is characterized by deterioration of internal wood. In transversal section the infected area is surrounded by a dark line. There are no manifestations on leaves while apoplexy strokes seem to be strictly connected. The proper esca is common in adult grapevines and consists in the presence of all symptoms. In all cases the infection is carried by spore produced by fruiting bodies which can be set on different kinds of plants far from vineyards. The contamination is favoured by rain. As pruning is the preferential portal for all kinds of fungi and remaining the pruning wounds vulnerable for a long time (3-8 weeks) it could be better to prune in winter months when there is a minimum of sporulation. There are no commercial products to control the different species of fungi, so the only possibility is preventing the attacks. Useful activities for prevention are good protection of pruning wounds with mastic and adopting treatments with Fosetyl-Al or with copper formulations that are able to reduce the symptoms on leaves. Also formulations that promote the production of phenolic compounds seem to reduce the symptoms. Instead the use of Trichoderma spp. may prevent the infection of healthy grapevines from Pch.