EPI model for management of grapevine downy mildew in Lombardy.

Grapevine downy mildew, caused by Plasmopara viticola, often requires numerous chemical treatments in order to reduce serious damages on leaves and clusters. The management strategy suggested by the Italian extension services is based on the occurrence of meteorological conditions suitable for P. viticola infections and the calculation of the incubation period. However various treatments executed following this strategy could be avoided in presence of low infection risk. EPI (Etat Potentiel d’Infection), an heuristic model designed for the assessment of infection likelihood of P. viticola, can be used to define a rational treatment strategy against the pathogen. The aim of this work is to compare the treatment schedule based on the EPI simulations with the extension service strategy in vineyards located in Lombardia, by assessing the corresponding infection indexes and the number of treatments applied in the different plots. Twenty experimental assays were carried out from 2008 till 2012 in Oltrepo Pavese, Valtellina, Sirmione (BS) and in the Mantova province, at Monzambano (MN) and Mantova (MN). In each experimental vineyard, the treatments corresponding to the two strategies were carried out in two plots, consisting of three rows, 80 m long. An analogous plot was not treated against P. viticola. The downy mildew epidemic development was assessed weakly in the untreated plots on 100 leaves and 100 clusters located in four subplots and at the end of the season on the treated plots. Each grapevine organ was classified in one of the following classes: 0- healthy; 1: 0.1-2.5 % symptomatic surface; 2: 2.5-5 % symptomatic surface; 3: 5-10 % symptomatic surface; 4: 10-25 % symptomatic surface; 5: 25-50 % symptomatic surface; 6: 50-75 % symptomatic surface; 7: 75-100 % symptomatic surface. The percentage infection indexes (I%I) per treatment and grapevine organs were calculated and compared using one-way ANOVA. The I%I assessed on the plots treat ed according to the different strategies were analogous, but the EPI strategies required a lower number of treatments. Overall, the treatment number was reduced by 57 % by EPI and in three vineyards no treatments were applied against P. viticola. Therefore the simulations obtained by using the EPI model represent a valuable indication for defining a sustainable and rational treatment schedule against P. viticola.