Vitis viniferais susceptible to phylloxera, an insect that attacks the roots of the vine and that caused terrible devastation at the end of the 19th century. The development of a graft onto an American rootstock that was resistant to phylloxera led to a vinestock that had the properties of its own grape family but roots that could not be infected by the insect. Vitis viniferais also susceptible to the leaf hopper that spreads the disease flavescence doree.
The species Vitis vinifera includes many varieties, known as cépages.Each wine-growing region has chosen the most suitable variety for its area, but economic conditions and the tastes of consumers can also play a part in modifying what is planted. Some vineyards produce wine from a single variety (for example, Pinot Noir and Chardonnay in Burgundy and Riesling in Alsace). In other regions (for example, in Champagne and Bordeaux) the greatest wines are the result of blending several varieties with complementary characteristics. The varieties are themselves made up of “individuals” (clones), which do not have identical characteristics (of productivity, rate of ripening, resistance to disease). The search is always on for the best stock. At the moment, research is being carried out into creating disease-resistant vines by genetic modification.
Growing conditions have a decisive effect on the quality of wine. It is possible to increase yields considerably by changing fertilization and pruning methods, choosing different stock and altering the density of the plants. It is not possible however to increase yields dramatically without affecting quality, except when nature intervenes; then quality is rarely compromised, and some of the greatest vintages have been produced from abundant harvests.
In recent years the increase in yields has been linked to better growing conditions. The advisable limit depends on the style of the wine: for good red wines the maximum advisable yield is between 45 and 60 hi per ha and a little more for dry white wines. To produce very good wines, you also need vines that are ten years old or more, with a well-developed root system.
The vine is susceptible to numerous diseases, various types of mildew and rot, which deplete the harvest and give the grapes a nasty taste, which is detectable in the wine. Wine-growers now have the means to treat these diseases effectively and this has certainly contributed to the general improvement in quality. In the past, a concern for security has probably led to an over-zealous use of chemical pesticides, but today they are used more prudently. In general, these chemical treatments are used only when absolutely necessary, and research within agricultural biology is now focusing on soil biodynamics, with the aim of creating natural conditions that will make the vine less susceptible to disease.