Development and evaluation of a bitter pit prognosis model in apple orchards in the South Tyrol (Northern Italy)

Bitter pit is the main nutrient-related disorder in several apple growing areas, including the South Tyrol (Italy). In this region, since 1985, when bitter pit severely damaged the fruit industry, the development of a prediction programme was undertaken, particularly focused on the K/Ca ratio in the young fruit. For 13 years fruit samples were taken in experimental orchards for analyses at the beginning of July, when the fruitlets have an average weight of 70 g. The main conclusions of the study indicate that the calcium and potassium concentrations in the fruit provided useful information about the risk of future development of bitter pit and other physiological diseases. When a threshold in the K/Ca ratio is reached in the fruit, growers are recommended to take special measures to prevent bitter pit such as increasing the number of calcium sprays.