Prospecting for new fungicides to control apple scab (Venturia inaequalis) in organic fruit growing

Summary

Apple scab (Venturia inaequalis (Cke.) Wint.) causes serious losses in quality and yield of organically as well as conventionally grown apples. Organic apple growers are highly dependent on the use of sulphur, lime sulphur and copper fungicides to control apple scab. Whereas only elemental sulphur is permitted for scab control in organic apple production in Denmark, and in addition lime sulphur in The Netherlands, copper fungicides are used in organic production in many European countries. However, the use of copper fungicides in the EU is now being phased out (EU Council Regulation (EEC) No. 2092/91) and alternative fungicides for control of apple scab and other diseases in other crops are increasingly needed. As part of the EU project REPCO (Replacement of Copper Fungicides in Organic apple and grapevine production in Europe, 2003-7) we are prospecting for plant extracts and other materials, including resistance inducers, to be used for apple scab control in organic fruit production. In the routine screening systems, potential materials are evaluated for control efficacy against scab on apple seedlings grown under controlled conditions in growth chambers. Promising compounds are further tested in small scale orchard experiments and finally trialled in a modern integrated organic orchard system, in which application of the compounds is combined with sulphur and other control measures. Several interesting materials have been identified as potential organic fungicides