Abstract
Many pesticides are used very effectively against fungal diseases in crop protection. However, the widespread use of synthetic pesticides in conventional fruit production clearly indicates that pesticides have several limitations and serious harmful effects on the environment and on human health. This prompted a serious need for a more environmentally benign view in the practice of fruit growing and particularly in plant protection, which also strengthened the concept of environment-friendly approach for apple. In this review article, the present status, possibilities and approaches towards fungal disease management for organic and integrated apple production systems, which are the most prominent environmentally friendly production systems of apple, are reviewed. The review focuses on the control of five important apple diseases: apple scab (Venturia inaequalis), apple powdery mildew (Podosphaera leucotricha), European canker (Nectria galligena), brown rot (Monilinia spp.) and the disease complex of flyspeck and sooty blotch. The first section of this study provides background information and basic features of current disease control in both apple production systems. Then, in the second section of this study, details of novel aspects of non-chemical control approaches against apple fungal diseases, including agronomic measures, mechanical, physical and biological control options as well as essential features of apple cultivar resistance to fungal diseases are given. The overview on five groups of agronomic measures: (1) cropping system and cover crop, (2) plant material and planting, (3) pruning and canopy management, (4) orchard floor management and (5) nutrient supply and harvest, and another five groups of mechanical and physical control methods: (1) pruning, (2) removal of inoculum sources, (3) shredding of leaf litter, (4) burying of inoculum sources and (5) flaming of leaf litter, showed that these non-chemical control measures are one of the most essential approaches for reducing the infection potential of inoculum sources in apple orchards. However, most of these methods are not widely spread in the apple-growing practice due to their high labour costs and/or time limits during the season. We showed that expert-system-based automatisation in the future may greatly enhance the effective integration of these methods into apple growing. We also described almost 30 biological control options, including antagonists, extracts/oils of plants and composts, which were explored recently against fungal diseases of apple, though only few of them are commercially available for the apple-growing practice. Most of these biological control options are suitable only for organic apple growing, as their effectiveness against the key fungal diseases is not able to fulfil the requirements for integrated apple orchards or they are not substantially cost-effective. Developing an effective biological control against polycyclic fungal diseases of apple will be a great challenge in the future for preharvest disease management programmes. In our literature analyses, host resistance, based on breeding programmes for multiple disease resistance, was evaluated as the greatest potential in the effective disease management of environmentally friendly apple production systems. Theoretically, aiming for complete host disease resistance would result in eliminating one of the basic elements of the epidemic triangle and omission of chemical control approaches from disease management of apple.
Published Version
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