Veins turn yellow and the leaves curl, vine shoots don’t lignify but remain limp and rubbery, clusters of grapes dry up and lose their precious juice. These are the feared symptoms of flavescence dorée, the grapevine disease which is disturbing the peace of mind of Italian growers and threatening their livelihoods.
The epidemic first appeared in the south of France between the 1960s and 1970s, then gradually spread over the whole of Europe. With varying intensity it now affects all growing areas around the 45th parallel. The disease is spread by a small insect, a leafhopper called Scaphoideus itanus, which sucks the sap from grapevines and transmits the phytoplasma causing the disease.
The problem remained a mystery for years but now the causes are understood and the way it propagates in the environment has been identified. There are still many aspects which are not clear however. It is not understood why it is so virulent in certain areas and definite solutions have not yet been found. When the disease appears, the only thing to do is pull out the vines. That is why it is increasingly common to see large holes breaking the regular rows of vines on planted hillsides.
For growers it is a scourge. Forced to replace the old vines with new ones, they have to work in a varying and irregular environment which makes all the vineyard work more arduous. Worst of all, the problem does not stop there: it is the youngest vines that are hardest hit and after spending time and resources to replace the vines, the new ones may again contract the disease. For small producers already suffering difficult market conditions, it is the last straw. The problem is widespread, vine nurseries can’t offer any guarantees and many growers are often in a quandary whether it is really worth replanting or if they should just leave things to their fate.
Various measures have been adopted to combat the problem. Attempts have been made to eliminate every possible center of infection, requiring uncultivated land containing vines to be controlled. In the worst hit areas legislation requires mandatory application of insecticide up to two or three times a year to curb the spread of the insect vector of the disease. Following apparently encouraging indications in the last two years, the situation is unfortunately again coming to a head. In their exasperation, growers suspect some producers are not pulling their weight in the fight against Scaphoideus titanus and everyone else is suffering the consequences.
If flavescence dorée has not received much attention, it is because the problem has so far not affected the best known wine production areas. But they too are now at serious risk and nobody can claim to be unaffected.
Fortunately the worst affected producers have received some financial help to replace their sick vines. It is now necessary to create greater safeguards against the spread of the disease and ensure that institutions cooperate more fully. Small producers are demanding that every effort must be made to control all the centers of infection and ensure that everyone is in fact playing their part in limiting the spread of the insect pest.
The final pressing demand is for the scientific community to dedicate more effort to finding a solution. We still do not properly understand the mechanisms controlling how the disease interacts with the soil, but studies examining how plant resistance to the disease relates to soil composition appear to offer some hope. It has been observed that some vineyards in areas severely affected by flavescence dorée initially displayed symptoms of the disease but it then disappeared.
It is thought it may be possible to help vines develop good resistance to external attacks through interaction with soil microorganisms which can produce substances effective against phytotoplasmas. We can only hope that by working along these lines, researchers will come up with answers to the wine sector’s growing concerns.
First printed in La Stampa on August 30 2005