Number and concentration of calcium nitrate plus Kelpak® sprays for control of bitter pit in 'Braeburn5 apple fruit

Abstract

In a spray trial to test the effects of calcium nitrate and a kelp extract (Kelpak®), fruit calcium (Ca) concentrations in ‘Braeburn’ apples peaked between 7.6 and 9.5 mg 100 g−1 fresh mass (FM) on 19 December 2000, then declined to between 2.3 and 3.2 mg 100 g−1 FM at harvest (22 March 2001). Fruit Ca concentrations on 19 December were highest where 12 sprays, each containing 117 g Ca per 100 I water were applied, without Kelpak®, at weekly intervals from 42 days after full bloom to 30 January. At harvest, fruit Ca in this treatment was no greater than where 12 sprays containing either 117 or 58.5 g Ca per 100 I water were applied with Kelpak®. Incidences of bitter pit in these treatments were, respectively, 1.0%, 1.3% and 3.4%. Where six half-strength sprays were applied, with Kelpak®, over the same time period, bitter pit increased to 9.3%. At harvest, fruit Ca concentrations were 0.25 mg Ca per 100 g−1 FM lower in pitted, than in bitter pit-free fruit. Total soluble solids and starch conversion were lower where 12 full-strength sprays were applied without Kelpak® than where 12 half-strength sprays were applied with Kelpak®. Starch conversion was greatest where six half-strength sprays were applied with Kelpak®. The effects on fruit colour of calcium nitrate, alone or with Kelpak®, were inconclusive