Predicting the date of budbreak of grapevine grown in the « Serra Gaucha » region

Predicting the date of budbreak allows a more organized and rational pruning, defining lire time for winter phythosanitary treatments and, if necessary, the application of products to improve homogeneous sprouting and to increase the percentage of budbreak. The objective of the work was to validate the predicting date of grapevine budbreak model developed by Pouget, in France, for the conditions of Bento Gonçalves, state of Rio Grande do Sul, Brazil. To achieve this purpose, daily meteorological data of air minimum and maximum températures (°C), from 1984 to 1999, were taken from the agroclimatological station located near the experiment. The phenological data of 20 grapevine cultivars were obtained from the Embrapa Grape and Wine Germoplasm Active Bank. The phenological évaluations for each cultivar were performed on six grapevines conducted in a high vertical trellis and pnined in a bounded double Guyot. For each year, winter pruning and cultural practices were done in the same date for ail cultivars. This methodology is based on the effects of température on the sprouting velocity, on the relationships between the sum of températures and the number of days up to sprouting, and between the precocity coefficient of sprouting and the sum of température. To obtain these relationships, the same cultivars used by Pouget were taken into account, being the June lst the date considered for the beginning of the sum of temperature. Results show that the methodology of Pouget may be applied either for the "Serra Gaucha" conditions, with the possibility to predict the date of sprouting with two or three weeks earlier, depending on the cultivar and on the year, which permit the grower a better winter pruning planning.