Evaluation of the of early powdery mildew control and the ascospores release in vineyards at Douro region

Abstract

Powdery mildew is the most harmful disease of grapevines in Douro region. To control this disease the use of fungicides takes a greater importance in different strategies. However there are not a consensus about the start and efficiency of the fungicide applications at the ascospores release, which occurs usually in February-March and the development of the disease during the season. The main objective of this work was to evaluate different treatment strategies in early phenological stages (stage 14 until stage 57) where the release of ascospores is greater. Also have the goal to contribute for the rationalizing the interventions in a steep slope vineyard, reducing treatments.

The experiment was conducted in the Douro Wine Region, in a vineyard located at Cima Corgo, with the cv Tinta Roriz (Tempranillo) during two seasons. The monitoring of the ascospores release started at the phenological stage “dormant bud”, using glass microscope slides. The experimental design consisted in four modalities with four replicates: 1T – control; 2T – three sprays with sulfour were applied starting at budbreak; 3T – sprays started at inflorescence fully developed (BBCH 57), which is the common practice in Douro, and the second spray was at pre-blooming and 4T – the spraying started only at pre-blooming with a DMI. After blooming all the treatments, with exception of the control, were sprayed at the same time with the same product. The severity of powdery mildew was assessed in grapes and leaves, based on the scale of OEPP (1981) in three different periods. At harvest proceeded to the evaluation of the percentage of powdery mildew (%), yield and fruit composition. Although the early release of ascospores, the disease development only begins near the flowering. The preliminary results reveal significant differences to the control, but no difference between the treatments 2T, 3T and 4T which move strategies to reduce the interest of the earliest sprays saving interventions in the vineyard.