Flavescence Dorée: Sizeable Reservoirs of the Disease around Vineyards

A formidable disease of grapevine, flavescence dorée continues to spread in Switzerland. The most recent knowledge acquired in Ticino allows us to better understand the role played in the risk of infection by gone-wild grapevines in woodlands around vineyards.

Flavescence dorée (FD) is a detrimental grapevine disease, which has become endemic south of the Alps and is spreading in the west of Switzerland. Currently, FD is still absent in the north and east of the country. Associated with a phytoplasma (cell-wall-less bacterium) transmitted by insect vectors, the disease causes dieback of the affected grapevines. Depending on the susceptibility of the grape cultivar, production losses and increases in vineyard management costs may be substantial. The phytoplasma associated with FD is a quarantine organism in Switzerland and the European Union. Consequently, there is an obligation to notify the competent authorities (i.e. the Cantonal Plant Protection Services) of symptomatic grapevines as well as an obligation to control the disease.

There is no known direct curative treatment of FD. The obligatory control measures consist in the application of insecticides against the main vector, the American grapevine leafhopper Scaphoideus titanus, the removal of the infected vines, and the use of certified plant material only. Despite these measures, the spread of FD continues.

Role of gone-wild grapevines in FD epidemiology

Funded by the FOAG, the project ‘FLAVID 2’ was conducted for three years under the auspices of the ‘Neobiota’ Competence Centre in Cadenazzo by WSL and Agroscope researchers. A scientific article recently published in the Journal of Plant Pathology sheds light on the complexity of FD epidemiology, which goes beyond the conventional model of “pathogenic agent – main vector – cultivated-plant host”. In particular, the results show that gone-wild grapevines growing in woodlands serve as reservoirs of the disease and as a habitat for its vectors. To contain the pathogen, proactive management of these habitats using a holistic landscape-management approach is essential.

Main results

• Insecticide treatments applied correctly and in a timely manner allow S. titanus populations in the vines to be reduced whilst preventing their migration towards low herbaceous plants. In these conditions, strips of vegetation inside the vineyard (inter-row) and between the vineyard and adjacent forests do not appear to constitute a potential haven for the main vector of FD.
• The polyphagous leafhopper Orientus ishidae, an alternative vector of FD, has been found occasionally in vineyards and regularly in the forest fringes adjacent to vineyards.
• Gone-wild grapevines are common in the forests in Ticino. Their establishment is mainly associated with the abandonment of winegrowing in difficult-to-manage locations and with land-use change.
• Certain gone-wild grapevines are infected with FD and harbour significant populations of S. titanus and O. ishidae. They may therefore constitute a reservoir of inoculum for the disease and a habitat for its vectors.
• Certain genetic profiles associated with FD and found in gone-wild and cultivated grapevines as well as in the two vectors of FD in Ticino have turned out to be identical.
• Hazel(Corylus avellana) has been confirmed as the preferred host plant of O. ishidae. The populations of this vector, which poses a potential danger for vineyards, can be effectively curtailed by reducing the presence of hazel as part of forest-margin management. This approach has a long-lasting impact and would not require regular annual management.