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Researchers have presented new findings on the vine disease flavescence dorée ("golden yellowing") and its vector, the American vine borer. The dreaded insects benefit from the warming climate in the north and in higher, cooler locations, but are contained in the south. Their eggs suffer at temperatures above 30 degrees Celsius, the adults above 40 degrees Celsius.
The cicadas are also much more mobile than previously assumed. The adults regularly cover distances of at least 400 metres. This finding leads the researchers to assume that fallow land or wild growth near cultivated vineyards could undermine the efforts of winegrowers in the fight against the disease, as the insects can hide well there.
According to studies in Bordeaux, the disease spread on average 17 metres per year from a source of infection. 80 percent of infections occurred within 22 metres of an infected vine. Infections decreased significantly at a distance of more than 50 metres. "We observe a fairly low dispersion, but a very efficient transmission of the disease," reports researcher Sylvie Malembic-Maher. In Champagne, seven hectares in Aisne were monitored. Here, 50 per cent of the infections occurred within a radius of 34 metres of a diseased vine, 80 per cent within a radius of 54 metres. The spread was therefore greater here. The probability of Chardonnay being infected is also almost twice as high as that of Pinot Noir and Pinot Meunier.
Another team of researchers investigated the chances of eliminating the vine cicada as a vector of the disease. In order to acquire the phytoplasma of the flavescence dorée, the insect requires two proteins as receptors. The team has observed that the production of these two proteins in the insect's cells can be reduced using the so-called RNA interference method. However, further investigations are still required.
A major problem with flavescence is that infected vines often only show symptoms after more than a year. It is therefore not enough to remove these vines, emphasises Sylvie Malembic-Maher: "Even if all symptomatic vines are removed, the disease spreads by being carried on by infected but non-symptomatic vines." It would be best to remove all vines within a certain radius of the infected vine. However, as this is hardly conceivable, uprooting and the fight against the cicada must be combined.
(al / source: vitisphere)