Grapevine sensitivity to fungal diseases: use of a combination of terroir cartography and parcel survey

In front of the economic interest and seeking to respect their environment, the wine growers move gradually towards a policy of reasoning their plant health protection. This is why, starting from epidemiologic studies on grapevine pathogens, forecasting models of the risks are developed by research and experimentation bodies. These models propose only a general diagnosis at the scale of the « small area » based primarily on the climatic variables related to the climate of the vintage. In the event of important risks, the professionals are sensitized and can protect their whole vineyard. However, secondary factors are also known to intervene on the sensitivity of the vine. Those are related to the soil, the surrounding landscape or the planting material and are characteristic of a reduced area of land. The present study seeks to (1) evaluate the effect of the secondary factors on the sensitivity of the vine and (2) to create some sensitivity maps in order to better forecast the mildew and powdery risks at the plot level. The used method is based on the combination of terroir cartography, parcel survey and expertise. The influence of cartographic variables on parasitic development has been tested by using statistical methods. The results indicate that, in the Loire Valley, soil is the main influential secondary factor that affects the plot sensitivity to mildew. In this respect, the weathering model « Roche-Altération-Altérite », developed by the Grapevine and Wine Research Unit of INRA (Angers 49, France) constitutes a pertinent index. For powdery mildew, the surrounding landscape has a marked effect on the plot sensitivity.