Studies on biological control of powdery mildew in cucumber (Sphaerotheca fuliginea) and rose (S. pannosa) by means of mycoparasites

Powdery mildew on rose ( Sphaerotheca pannosa ) and cucumber ( Sphaerotheca fuliginea ) are two serious diseases in glasshouses. Intensive control by fungicides is needed. The research presented here deals with biocontrol of powdery mildew on cucumber and rose by means of mycoparasites.

The mycoparasites Ampelomyces quisqualis , Sporothrix rugulosa and Tilletiopsis minor and Verticillium lecanii were tested on rose powdery mildew. V. lecanii produced the best results. For biocontrol at glasshouse scale an efficient production method of phialoconidia of V. lecanii was developed. In exploratory glasshouse experiments V. lecanii was superior to S. rugulosa in controlling cucumber mildew. Especially on a partially resistant cucumber cultivar biocontrol by V. lecanii showed prospect.

To identify characteristics for the selection of V. lecanii isolates with high potential for biocontrol under glasshouse conditions, effect of water limitation on 14 isolates was explored. Conidial germination, growth and sporulation were all clearly affected by humidity, but showed no correlation with mycoparasitic potential. The effect of timing the biocontrol treatment by V. lecanii was studied on rooted mildewed cucumber leaves. At high humidity early preventative and early curative treatments gave considerable reduction in mildewed leaf area. In semi-commercial glasshouse experiments our V. lecanii isolate, A. quisqualis and Sporothrix flocculosa were tested against cucumber powdery mildew.

A. quisqualis did not control the disease. V. lecanii had only minor effects. S. flocculosa gave the best control. The failure of biocontrol by V. lecanii was attributed to low humidity in the glasshouse. Formulation of V. lecanii with arachid oil significantly reduced its humidity dependence. Possibilities for integrated control are combinations of partially resistant cultivars, formulation of V. lecanii and combination of V. lecanii with fungicides.