Effect of foliar Zn, form and timing of Ca sprays on fruit Ca concentration in new apple cultivars

The semi-arid apple growing region of southern British Columbia has periodic problems associated with low fruit Ca concentrations and also chronic Zn deficiency. Current grower recommendations include multiple sprays of CaCl2 late in the growing season in years when fruit Ca problems are anticipated. Nevertheless, there is a constant search for methods to ensure effective application of Ca, especially for new apple cultivars. This research summarizes the cumulative results of a series of randomized, replicated spray trials undertaken in research and high density apple orchards. The objectives were to test the effectiveness of: (1) multiple postbloom Zn sprays, and (2) multiple postbloom Ca sprays, and (3) multiple late season Ca sprays of alternate formulation, relative to standard Ca recommendations as they affect fruit Ca concentration and quality at harvest. (1) Over 3 years in a ‘Jonagold’ orchard, 2 and 5 sprays of ZnTrac (2 ml/L) applied postbloom increased fruitlet and fruit Zn concentration from chronically low values, but harvest fruit Ca concentrations were more effectively increased by Ca sprays directly to the fruit. (2) In 7 years of trials conducted in ‘Fuji’, ‘Jonagold’ and ‘Gala’ orchards, 3-5 CaCl2 sprays (0.5% CaCl2 w/v) applied in the month postbloom significantly increased fruitlet Ca concentration in 4 of 7 occurrences. Only once were these fruit Ca increases measurable at harvest. In contrast, 4-5 CaCl2 sprays, 4-6 weeks prior to harvest usually (6/7 times) increased fruit Ca concentration. In a ‘Braeburn’ orchard, prone to bitter pit, 5 weekly early season (June 22-July 20) CaCl2 sprays were similarly less effective at increasing fruit Ca concentration but more effective at reducing bitter pit incidence than 5 weekly late season (Aug 25-Sept 22) CaCl2 sprays. (3) Multiple (4-6) applications of Nutrical and Calcimax Ca sources of recommended rates in late season did not increase harvest fruit Ca when tested in 2 orchards. Their effectiveness was similar to CaCl2 when the same amount of Ca was applied.