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Grapevine flavescence dorée symptoms © Sandrine Eveillard

Grapevine flavescence dorée

Flavescence dorée: monitoring natural reservoirs is a group effort

INRA researchers have developed a tool for comparing the efficacy of flavescence dorée monitoring systems and control efforts in four of France’s major wine-producing regions. The aim is to account for pathogen transmission risks attributable to wild plant species found near vineyards.

By Pascale Mollier et Sylvie Malembic-Maher, translated by Jessica Pearce
Updated on 07/04/2017
Published on 07/22/2016

Flavescence dorée, a type of grapevine yellows, is a serious disease that is caused by a phytoplasma (1). It is vectored throughout France and Europe by a leafhopper (2). When an outbreak of flavescence dorée occurs, quarantine regulations must be implemented immediately, resulting in major economic and environmental impacts (e.g., the increased use of insecticides targeting the vector). The situation is also difficult for grape growers, who may chafe at the mandatory control measures (e.g., ripping up infected vines and applying pesticides). Consequently, properly coordinating control efforts requires accounting for how stakeholders will react and respond when grapevines are being threatened.

Disease prevention and regional differences in control efforts

In more than half of France’s wine-producing regions, grape growers are required by national law to actively engage in collaborative efforts to fight flavescence dorée. However, the specific measures taken may differ according to many factors, such as the region, wine designation of origin, socioeconomic conditions, industry structure, and disease intensity.

For example, monitoring efforts are more intensive in certain regions because there is a great desire to reduce the impact of flavescence dorée. The number of treatments and the total area treated are carefully calculated, and measures can be customized depending on further risk evaluation.

Control measures, which take place at the vineyard level, are expanding to account for the disease’s ecology, including its occurrence in several habitat types, including agroecosystems.

Wild plant populations serve as reservoirs

Previous genetic studies have shown that the phytoplasma strains responsible for flavescence dorée are European in origin and existed in wild plant species, such as alder and clematis, before spilling over into grapevines. “Feral” grapevines are frequently found along the edges of vineyards and can also serve as reservoirs for insects and the phytoplasmas the latter vector.
Wild plants and feral vines are known to increase epidemiological risks. Yet, at the same time, they provide ecosystem services to cultivated vineyards. For instance, they serve as a reservoir for biodiversity, including species that are the natural enemies of pest species (3). It is therefore crucial to carefully consider the trade-off between the epidemiological risks and the ecosystem services that are associated with such semi-natural habitats.

Research groups in four French regions

Collecting leafhoppers on alder trees bordering a vineyard; the insects were used in experiments examining phytoplasma vectoring dynamics.. © INRA, Sylvie Malembic-Maher
Collecting leafhoppers on alder trees bordering a vineyard; the insects were used in experiments examining phytoplasma vectoring dynamics. © INRA, Sylvie Malembic-Maher

Four research groups involving major players (4) in the fight against flavescence dorée have been set up in four French regions that are differentially affected by the pathogen: in Burgundy and Provence, where the disease is emerging; Bordeaux, where it is firmly established and outbreaks are recurrent; and Alsace, from which it is absent for the moment.
These groups are surveying wild plant species that could serve as reservoirs, monitoring vectors, collecting samples, and running experimental trials that examine vector dynamics and the efficacy of using the pathogen’s natural enemies to combat disease within vineyards.

In addition to the above participatory science, certain groups are also working to account for the epidemiological risks associated with wild plant reservoirs: they have created tools for monitoring the pathogen and customizing control efforts.

 Control success depends on stakeholder unity

Sociological research has also been carried out to characterize the joint efforts underpinning mandatory regional and departmental control efforts; interviews have been conducted, participant observations have been collected, and archives have been studied. One of the conclusions that has emerged is that the success of control measures depends on the cohesiveness of the wine industry’s network of stakeholders and the degree to which those organizing and managing collaborative efforts to combat the pathogen strike just the right balance between economic considerations and the implementation of government regulations.

Given that wine producers are focused on short-term economics, it is tricky to expand control efforts to include wild species, since, strictly speaking, they fall outside the vineyard’s boundaries and thus grape growers’ normal range of considerations. However, more and more information is becoming available on the ways in which such species specifically contribute to disease risk, and management tools are taking an ever more ecological approach to the disease. Such advances are being integrated into experimental approaches carried out by research partners and are influencing the formulation of regulations. However, they remain rather difficult to apply in more general ways.

(1) Phytoplasma: a bacterium belonging to the taxonomic class Mollicutes, which contains obligate parasites without cell walls

(2) Scaphoideus titanus

(3) Natural enemies of grapevine pests

(4) The Fladorisk Project (June 2014–December 2016). The groups have brought together stakeholders involved in the fight against flavescence dorée (SRALs, FREDONs, technical organizations, nursery owners, and representatives from pilot vineyards) as well as organisms responsible for environmental resource management (e.g., city halls and natural parks). The groups were led by researchers from three INRA research units: SAVE, BFP, and LISIS.