Efficacy of the biocontrol agents Bacillus subtilis and Ampelomyces quisqualis applied in combination with fungicides against powdery mildew of zucchini

The activity of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides against Podosphaera xanthii on zucchini was tested in five experimental trials carried out under greenhouse conditions. The population of P. xanthii used throughout the work for artificial inoculation was able to cause slight infections on zucchini plants treated with the field dosages of azoxystrobin and penconazole. B. subtilis when combined with azoxystrobin against P. xanthii at the recommended field dosages provided better powdery mildew control than the two control measures alone. Such results were consistent throughout the different trials. A similar synergistic effect was shown by the combination of A. quisqualis with myclobutanil: however, in this case, more studies are necessary to confirm the consistency of that phenomenon. The results obtained in this study support the possibility of a synergistic effect among the biocontrol agent B. subtilis and QoI fungicides. Such interaction is very interesting because of the presence of resistance towards QoI in the populations of P. xanthii.