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Commercial-Scale Control of Rose Powdery Mildew with a Fungal Antagonist. R. R. BELANGER, Assistant Professor, Departement de phytologie, Faculte des Sciences de l’griculture et de l’Alimentation, Universite Laval, Quebec, Canada G1K 7P4. C. LABBE, Research Assistant, Departement de phytologie, Faculte des Sciences de l’Agriculture et de l’Alimentation, Universite Laval, Quebec, Canada G1K 7P4; and W. R. JARVIS, Senior Research Scientist, Harrow Research Station, Agriculture Canada, Harrow, Ontario N0R 1G0. Plant Dis. 78:420-424. Accepted for publication 20 January 1994. Copyright 1994 The American Phytopathological Society 420. DOI: 10.1094/PD-78-0420.

The yeastlike fungus Sporothrix flocculosa, reported to be antagonistic against several members of the Erysiphales, was used under strict commercial conditions to control rose powdery mildew caused by Sphaerotheca pannosa var. rosae. The antagonist was applied in two separate trials on nearly 1,000 plants of rose cultivars Preference and Samantha, and results were compared with those obtained from plants treated with registered fungicides. In the first trial, treatment with the antagonist exerted control comparable to that of the fungicide, but its efficacy varied with the level of relative humidity prevailing in the greenhouse. In the second trial, S. flocculosa was again as effective as fungicides at controlling powdery mildew, and amendment of the antagonist suspension with a surfactant to reduce dependency on humidity yielded even better results than S. flocculosa alone or fungicides. The quality of harvested roses was similar following either chemical or biological treatment in cv. Samantha and was higher following biocontrol treatment in cv. Preference.