Organic pome fruit production in Europe and the difficulties in control of fungal diseases

Abstract: Apple and pear production is localized in specific regions within Europe. As differentas their climatic conditions, as special are their production requirements. The severe restrictionson the use of plant protection products in organic farming imply that not every fruit growing areais suitable for organic pome fruit production. Considering the susceptibility of different crops andvarieties to fungal diseases is therefore a basic principle for effective organic production systemsin most growing areas. European regulation constitutes the legal framework for the registration ofactive substances of plant protection products within the EU, but each substance and commercialproduct must then be authorized on a national level. Copper- and sulphur-based products as wellas lime sulphur, used in targeted spray programs, are most commonly applied for the control offungal diseases such as apple scab and powdery mildew. In some countries, mainly in thenorthern part of Europe, copper and lime sulfur are not registered. In other countries lists of socalledplant strengtheners, not regulated by the EU and containing active substances withfungicidal (side) action (for example acid clays, carbonates and phosphonates), exist. At themoment the continuity of these lists is uncertain. The main fungal diseases, scab (Venturiainaequalis) and powdery mildew (Podosphaera leucotricha), certainly are a real challenge fororganic pome fruit production, and their biology and control strategies have been studiedextensively and almost exclusively over the last 15 years (MacHardy, 1996; Holb, 2007;Chapman et al., 2011). However, also the so-called secondary fungal diseases such as alternariablotch (Alternaria mali), sprinkler rot (Phytophtora spp.), bull’s eye rot (Pezicula malicorticus),sooty blotch (complex of different fungi), white haze (Tilletiopsis spp.), etc. (Weber, 2009; Baricet al., 2010; Mayer et al., 2010), are increasingly becoming of concern. These diseases, with theirorigin and development mostly unexplored, used to occur occasionally, but are now appearingwith increasing frequency and intensity. Therefore, an urgent need for the development of newcontrol strategies against these “new” fungi, compatible with organic farming, exists.