COMMERCIAL-SCALE CONTROL OF ROSE POWDERY MILDEW WITH A FUNGAL ANTAGONIST

The yeastlike fungus Sporothrix flocculosa, reported to be antagonisti c against several members of the Erysiphales, was used under strict co mmercial conditions to control rose powdery mildew caused by Sphaeroth eca pannosa var. rosae. The antagonist was applied in two separate tri als 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 antagon ist exerted control comparable to that of the fungicide, but its effic acy varied with the level of relative humidity prevailing in the green house. In the second trial, S. flocculosa was again as effective as fu ngicides at controlling powdery mildew, and amendment of the antagonis t suspension with a surfactant to reduce dependency on humidity yielde d even better results than S. flocculosa alone or fungicides. The qual ity of harvested roses was similar following either chemical or biolog ical treatment in cv. Samantha and was higher following biocontrol tre atment in cv. Preference.