Sylvie Malembic-Maher

Researcher at the Fruit Biology and Pathology Research Unit at INRAE-ISVV

Published in "Terre de vins*"No. 66 – July/August 2020

What is flavescence dorée?

It is a vine disease caused by tiny parasitic bacteria, known as phytoplasmas, which multiply in the sap of the vines and disrupt their metabolism. The bacterium is transmitted between plants by a piercing-sucking insect, the leafhopper Scaphoideus titanus, through the exchange of infected plants or via grafting. It was first observed in France in the 1950s and subsequently spread throughout southern Europe. This quarantine bacterium causes yellowing or reddening of the leaves, leaf curling, shoots that remain green and limp, and the withering of the bunches, leading to a reduction in both the quantity and quality of the harvest and, ultimately, the death of the vine.

Flavescence dorée is a vine disease transmitted by a leafhopper, causing the vines to wither. As there is no cure, control measures rely on monitoring, prevention and the grubbing-up of infected vines.

Are we witnessing a resurgence of flavescence dorée in France and Europe, possibly linked to climate change?

There has been no increase in the impact of the disease in terms of crop losses in recent years, but rather a continued spread of the insect and the disease to vineyards that were previously free of the disease, including those furthest north. The impact of climate change, however, is not yet fully understood. We know only that mild winters and hot summers, with thermal and water stress, are unfavourable for the leafhopper, whilst rising temperatures in spring and early summer promote the proliferation of the bacterium, which has an optimal growth temperature of 26 °C.

What are the latest developments and research advances in the fight against flavescence dorée?

The research initially focused on characterising the disease cycle and the biology of its insect vector. Before the introduction of the leafhopper – which was imported from North America during the phylloxera crisis – the bacterium was already naturally present on the European continent in plants surrounding vineyards, without causing any damage to the vines. It was the introduction of the leafhopper that led to the first outbreaks. The only known control measures are preventative: monitoring vineyards and nurseries to detect diseased vines as early as possible; grubbing up diseased vines or even the entire plot if more than 20 per cent is infected; and insecticide treatments against the leafhopper...

We have developed diagnostic tests that enable the detection of the bacterium in vines and the identification of the different strains circulating within European vineyards.

Several projects are also working on detecting the symptoms of the disease through image acquisition in vineyards using satellite systems, drones or detection systems mounted on tractors. There are no known resistant grape varieties, but we have shown that certain grape varieties are less susceptible to the disease and limit its spread.