Toward an Integrated Use of Biological Control by Cladosporium cladosporioides H39 in Apple Scab (Venturia inaequalis) Management.

Apple scab, caused by Venturia inaequalis, is the most important disease in apple production, reducing yield and quality of fruit. Control of apple scab in commercial orchards currently depends on multiple applications of fungicides. The potential of the antagonistic isolate Cladosporium cladosporioides H39, originating from a sporulating colony of V. inaequalis, to control apple scab development was tested in eight trials during 2 years in orchards in Eperjeske (Hungary), Dabrowice (Poland), and Bavendorf (Germany) planted with different cultivars. Treatments were conducted as calendar sprays or after infection periods. Additional trials in an orchard in Randwijk (The Netherlands) focused on the effect of timing of antagonist application before or after infection periods. The overall results of the field trials consistently showed-for the first time-that stand-alone applications of the antagonist C. cladosporioides H39 can reduce apple scab in leaves and fruit. This was demonstrated in an organic growing system as well as in conventional orchards by spray schedules applied during the primary or the summer season. In both systems, the same control levels could be reached as with common fungicide schedules. Efficacies reached 42 to 98% on leaf scab incidence and 41 to 94% on fruit scab. The antagonist was also effective if applied one or even several days (equivalent to approximately 300 to 2,000 degree h) after infection events in several field trials and a trial conducted in Randwijk with single-spray applications at different intervals before or after infection events. Better understanding of the biology of the antagonist will help to further exploit its use in apple scab control.