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Disease Note

Powdery Mildew (Erysiphe cichoracearum) of Greenhouse Lettuce in Ontario. B. N. Dhanvantari and W. R. Jarvis, Agriculture Canada Research Station, Harrow, Ontario N0R 1G0. Plant Disease 69:177, 1985. Accepted for publication 31 October 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-177g.

A greenhouse crop of butterhead lettuce (Lactuca sativa L.) cvs. Salinas, Ostinata, and Revel at Aylmer, Ontario, was found to be infected by powdery mildew in December 1983.  The disease was first observed when the crop, which was grown under the nutrient film technique, was nearing harvest.  Both surfaces of the older leaves were extensively covered with mycelium and conidiophores, and in the advanced stages of the disease, the leaves showed scorch symptoms.  The conidia, in chains, were mostly ellipsoidal to elongate-doliiform, 25–38 μm long and 12–18 μm broad (mean 29.5 × 16.5 μm), and conformed to Erysiphe cichoracearum DC.; they did not contain fibrosin bodies.  The perfect stage was not found.  This is the first report of powdery mildew on lettuce, either in the greenhouse or in the field, in Canada.

References: Crute, I. R., and Burns, I. G. Plant Pathol. 32:455, 1983.  Schnathorst, W. C., et al. Phytopathology 48:538, 1958.