Phenological models for prediction of veraison and harvest in grapevine

The objective of this study was to develop phenological models capable of predicting the onset of veraison and harvest in grapevine early enough to be useful for viticultural activities planning. Models are based on the responsiveness of phenological timing to the preceding thermal conditions. Key temperature variable and period for the onset of veraison and harvest were determined using the long-term (1981-2007) temperature and phenological data for 20 wine cultivars grown in the region of Sremski Karlovci (Serbia). The input variable for both phenological models was the maximum daily temperature averaged over the period from April 1 to June 30. The general model equations set up for grapevine as a species were adjusted for each cultivar by adding a correction factor. The correction factor was calculated as a difference between the mean date of phenological stage onset for given cultivar and the average value for all examined cultivars. The proposed empirical models proved to be capable of predicting the onset of veraison and harvest in grapevine cultivars with high accuracy, up to one and half month ahead for veraison and up to three months for harvest. On average for all cultivars, the mean absolute differences between the observed and predicted veraison and harvest dates were 4 and 6 days, respectively. The results are very satisfactory, having in mind the high year-to-year variability of veraison date (up to 49 days) and harvest date (up to 64 days) during the studied period