Agrometeorological simulation of grapevine growth and response to disease stresses.

Differences in crop growth between years or locations may be explained by differences in the amount of ligth received by the crop and in water or nutrient supply. However, variation in crop growth rate and yield may also be caused by the presence of reducing factors, such as pests and diseases. In this case, the size of yield reduction depends on the plant processes affected by injury components, the growth rate of the healthy crop and the timing and intesity of growth reduction. Dynamic crop models offer a valuable framework to structure thinking about the interactions between growth reducing factors and crop growth processes under variable environmental conditions. The objective of this study was to use experimental data (i.e. growth and physiological measurements) collected in untreated and control plots for modelling biomass accumulation and yield of grapevine (Vitis vinifera) plants affected by downy (Plasmopara viticola) or powdery mildew (Unicinula necatrix). A mechanistic simulation model grapevine growth was coupled to disease models to evaluate the effects of these pathogenes on grapevine. Field data were used to quantify the effects of mildews on crop physiology, to calibrate model parameters and to validate the integrated models for yield of diseased plants. The results were discussed in order to evaluate the application of this approach for assessing economical threshold for fungicide applications according to infection level and crop conditions. The real benefit for vine-growers was also discussed.