The virus in the vineyard…

When one drives nowadays in the winelands the beautiful red coloured leaves of vineyard are all around us.  However, as the old saying goes, beauty is in the eye of the beholder and these colours are unfortunately not so appealing to grape and wine producers as it is usually a sign of a virus infection in the vines. Now before I go any further you can relax, the virus that causes these colours is called the leave roll virus and while it affects grapevines it’s completely harmless to us as humans. However, it is not something that produces want in their vineyard. The reason for this is that it actually makes the plant sick over time as well as influence the quality and quantity of grapes produced.

When the plant gets infected with this virus it leads to the vine producing less sugar and colour compounds in the grapes compounds (remember the anthocyanins I wrote about last time), the grapes gets ripe slower, and leads to less grapes being harvested by the producer. The red colours of the leaves are more obvious in red grape cultivars than in white cultivars.  These negative grape aspects are then also reflected in the resulting wines, depending on the degree of infection. In the following figure an infected vine can be seen on the right, while its healthy neighbour on the left does not show any symptoms. It is also clear that the red wine on the right made from infected vines has less colour. We are currently busy with research to assess this and other effects the leaf roll virus have on wine quality.

virus pictures

Previous research has shown that the leaf roll virus can spread very rapidly, from one infected plant to a whole vineyard within a few years if left unchecked. Last time I checked vines cannot sneeze like we do, so how does it actually spread you might wonder? The virus is mainly spread by vectors of which the mealy bug is the main culprit. Vine producers can thus either control these little buggers (the mealy bug, also known as Planococcus ficus) or ensure that they plant only heathy, virus free vines planting material. However, even this healthy vines can infected by the leave roll virus at a later stage from infected neighbouring vineyards of farms, so continued monitoring is essential. Infected plants thus need to be removed continuously. When the virus infection reaches a certain percentage it is advisable to remove the whole vineyard and replace it with new healthy vines. It is then advisable that all roots left in the soil are removed and treated with insecticides and that the soil is left fallow for at least one season so that the mealybugs carrying the virus can die off. Fortunately the South African wine industry through Winetech has invested significantly in research on leave roll virus and we are currently seen as one of the world leaders on addressing this problem. It thus seems that the tide is turning to fix this problem in our industry. So next time you drive through our vineyard, remember that more red in a vineyard does not always equate to more red in the glass…

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