There is a lot of talk about fungal diseases, which are a real problem for winegrowers (powdery mildew/oidium, downy mildew/mildiou and others). But other diseases in the vineyard are also serious. One is flavescence dorée (grapevine yellow in English), a bacterial infection spread by a grasshopper. A November seminar organised by the French research institute INRAE gave us some interesting information.
The grasshopper came to Europe at the beginning of the 20th century. American vines were imported from the United States, and the grasshopper tagged along for the ride. The bacterium, however, was already present in Europe but not the insect. The combination did not turn out well. Flavescence dorée was first discovered in Armagnac in 1958, and since then, the grasshopper has spread the bacterium around Europe.
An alarmingly large part of the French vineyard area is infected. It is not certain that the vines will die, and it may take time, but they will weaken. It is essential to carefully monitor the vineyards and uproot infected vines so they do not spread the disease further. Furthermore, spraying with insecticides against the grasshopper is vital; in several regions of France, spraying is mandatory.
All grape varieties can be affected by flavescence dorée; currently, none are resistant, but they are more or less sensitive. It is in that way a bigger threat than the fungal diseases. Malbec, merlot and syrah are only slightly susceptible, but other widely planted varieties such as cabernet sauvignon, chardonnay, grenache, sauvignon blanc and ugni blanc (in Cognac mainly) are very sensitive.
