New Zealand Plant Protection 69 (2016): 230-237
Postharvest foliar nitrogen (urea) is often applied to apple leaves immediately after picking for bud fertilising, and/or during leaf fall for Venturia inaequalis control. During 2013-2016, ethylene diamine tetra-acetic acid copper (EDTA-Cu, to enhance leaf abscission), urea, calcium nitrate and Bud-Wiserô foliar treatments were applied alone or in combination to determine their effects on leaf scar infection by Neonectria ditissima in 'Braeburn' (2013-14), 'Scifresh' and 'Royal Gala' (2015-16) orchards. In 2013-14, leaf scar infection increased six-fold when 5% urea was added to EDTA-Cu and sprayed at the onset of leaf fall. In 2015-16, up to a nine-fold increase in leaf scar infections was observed. The timing of application was more important than the amount or form of nitrogen used. As a result of this research, the use of urea-based foliar nitrogen fertilisers for V. inaequalis before leaf fall are not recommended, and growers should consider all factors affecting Neonectria ditissima infections before applying nitrogen immediately after harvest.
Keywords: European canker, Nectria galligena, fertiliser, picking wound.
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Copyright © 2016 New Zealand Plant Protection Society (Inc.).