Scab control in organic apple production: conclusions of an eight-year studyin temperate weather conditions


Abstract: The objective of this study, conducted over eight growing seasons (2002−2009), is toidentify an innovative way for reducing the use of fungicides and in particular, copper fungicides,for the control of apple scab (V. inaequalis) in organic apple production. Special emphasis is puton cultivar traits, sanitation practices and primary scab infection control during spring season. Anoriginal approach is proposed for defining a specific spray timing involving spraying during theinfection processes, especially before fungal penetration, determined by the RIMpro softwarewarning system. This ‘during-infection’ spray strategy allows reducing from 30 to 50% theamount of fungicide usually used for effective apple scab control, on high scab-susceptiblecultivars. Potassium bicarbonate, lime sulphur, and three plant extracts such as peel orangeextract, among 60 alternative products tested, have the potential to reduce copper use. However,copper use, even with low doses, seems to be still necessary in presence of scab-susceptiblecultivars. The results obtained in these experiments could not be attributed to the specifictechnical performances of the tunnel sprayer used, which however, offer valuable environmentalbenefits. This work shows that (i) planting cultivars with polygenic scab-resistance traits, (ii)increasing accent on sanitation practices aimed at reducing initial inoculum in autumn, and (iii)applying an accurate “during-infection” spray strategy in spring, are the three most promisingapproaches for substantial further reductions in protection products fully compliant withinternational organic crop production standards.

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