Non- Chemical Management of Apple Scab- A Global Perspective

Apple scab, caused by the fungus Venturia inaequalis (Cooke) G. Wint. is the most widespread disease in apple orchards worldwide. In order to manage apple scab and produce a marketable crop, growers across the globe have relied on 10 to 18 applications of synthetic chemicals at an annual cost of US$202 to $506 per hectare. Until recently, fungicidal control was perceived as the only economical control measure but this perception is changing because of the high costs of new molecules such as the strobilurine-based fungicides, increased fungicide resistance in populations of V. inaequalis, and increased appreciation of environmental costs and consumers negative perceptions of fungicide use. For all these reasons cited above, interest is increasing to develop alternative strategies to manage apple scab. These changes include re-designing orchards so that cultivars with differential susceptibility can be treated with fungicides based on different schedules and using post-harvest treatments, such as leaf shredding or application of biological control agents. New knowledge of the resistance mechanisms in Malus may also present new management options. Despite the increased complexity of integrated scab management, it can prove more sustainable as it involves the use of more than one method and reduces the risk of development of resistance to fungicides in the pathogen population. Ultimately, sustainability will depend on the cost effectiveness of integrated approaches as compared to total dependence on fungicides to control apple scab.