Challenges and prospects for integrated control of powdery mildews in the greenhouse

Over the years, powdery mildew diseases have been managed mainly by chemical fungicides, but recent reports have high-lighted the potential of biological and other prophylactic methods as alternative strategies of disease management. For instance, a yeast-like fungus, Sporothrix flocculosa, was found to be a powerful antagonist of powdery mildew fungi, with potential for commercial utilization. Microscopic and chemical studies revealed that S. flocculosa acted rapidly against its target hosts by means of antibiosis. When tested in large-scale experiments, S. flocculosa was as effective as fungicides in controlling rose powdery mildew. However, it is well known that biocontrol agents often become less effective when disease pressure is high, hence it is necessary to integrate other approaches to support biocontrol methods. In this context, we have isolated, by selection pressure, a new strain of S. flocculosa with resistance to dodemorph-acetate, a fungicide recommended for control of rose powdery mildew. This strain was shown to be as effective as the wild type at colonizing powdery mildew when used alone or in combination with the fungicide. In addition, in the case of cucumber powdery mildew, S. flocculosa was found to be compatible with prophylactic methods such as soluble silicon and extracts of Reynoutria sachalinensis as a component of an integrated program that may lead to successful repression of the disease without fungicides.