There are several known mycoparasites of cucumber powdery mildew that could potentially be used for biological control in greenhouses. Sporothrix rugulosa and Verticillium lecanii were the most promising of several species tested in lab experiments on detached leaves or young plants. These fungi were then tested for their ability to control cucumber powdery mildew under greenhouse conditions on cucumber varieties with varying levels of resistance to mildew.
V. lecanii (formulations of which are commercially available in Europe for biocontrol of aphids and whiteflies) controlled mildew better than S. rugulosa on both susceptible and partially resistant cucumber plants.
The mildew fungus grew twice as fast and produced more spores on the susceptible plants; the mycoparasites were much more effective against the slow-growing mildew colonies than fast-growing ones. On the partially resistant cultivar (Flamingo), V. lecanii was able to keep the disease below 15% infected leaf area. In this case, the mildew was given one week to develop before application of treatments. Control might be even better if biocontrols are applied earlier.
If applied to a partially resistant variety, V. lecanii is an effective candidate for biological control of cucumber powdery mildew. Selection of isolates with a higher control potential and research into different formulations (especially for use under low humidity conditions) could improve the efficacy of this mycoparasite and lead to commercialization.
Verhaar, M. A., T. Hijwegen, and J. C. Zadoks. 1996. Glasshouse experiments on biocontrol of cucumber powdery mildew (Sphaerotheca fuliginea) by the mycoparasites Verticillium lecanii and Sporothrix rugulosa. Biol. Control 6: 353-360.
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