Application of alkylresorcinols in an organic apple orchard for protection against storage diseases

Each year, fungal storage diseases destroy large amounts of apple, especially in organic orchards. In the present study, antifungal activity of a rye bran-based remedy with 5-n-alkylresorcinols (ARs) was investigated. In 2014 and 2015, ‘Amorosa’ apple trees in an organic orchard were sprayed with a 0.025% AR emulsion pre-harvest, once or twice at different points in time. In addition, emulsions with different AR concentrations were applied postharvest on fruit inoculated with three different fungi (in vivo) and on fungal mycelium and conidia (in vitro). Fruits from trees sprayed in August and/or September had significantly less fungal decay in comparison with fruits from unsprayed trees, both at harvest and after storage in regular air and in controlled atmosphere condition (CA). Effects on fruit quality were small and inconsistent whereas yield was significantly reduced, especially after early-season applications (June, July). Yield was, however, similarly reduced when a reference emulsion without ARs was applied suggesting that this effect was not brought about by the ARs. The in vivo and in vitro experiments showed that anti-fun-gal activity increased with higher AR concentrations. Further experiments with late-season applications and higher AR concentrations should be undertaken