Articles
VINEMILD: AN APPLICATION-ORIENTED MODEL OF PLASMOPARA VITICOLA EPIDEMICS ON VITIS VINIFERA
It affects leaves and clusters and beside destruction of the infected tissues, losses result also through a reduction of yield quality.
The European cultivars being highly susceptible, favorable climatic conditions for the development of the fungus can result in a total loss of the crop.
Since the discovery of the Bordeaux mixture, the disease has been therefore controlled mainly chemically in a preventive way.
However, in years with unfavorable conditions, the disease may appear only late, causing no or little damage.
Still, in a protective spraying scheme, the number of sprays will be the same.
Considering the explosive and destructive character of the disease, the potential risk of loss resulting from an incorrect control strategy is in no relation to the gain from a reduced number of fungicide applications.
Therefore, growers will only accept to reduce fungicide applications if they have the guarantee that the risk of an epidemic development of the disease is very low.
There is however a pressure on growers to avoid unnecessary pesticide applications and consequently a demand for tools such as decision aids allowing to apply only necessary sprays.
Being confronted with this demand in the mid-eighties, we evaluated two models in use at that time, one in France and one in Germany, but none satisfied our requirements so that we initiated the development of a new one.
Our requirements, beside accuracy, were biological soundness, flexibility and expendability.
Biological soundness was required because we were convinced that reduction of fungicides to the minimum requested a thorough understanding of the system.
The development of an empirical model, which would have led to more immediate results, was therefore not taken in consideration.
Flexibility and expandability were direct consequences from the fact that Swiss vineyards vary greatly due to the significant variations of the geotopographical environments: beside the use of different cultivars, planting density may vary from 4000 to 12000 plants per ha with different training and soil cultivation techniques while annual rainfall can be 500 mm in one location and 1500 mm in another.