Disease Note

Cleistothecia of Sphaerotheca fuliginea on Cucumber in Ontario. W. R. Jarvis and K. Slingsby, Agriculture Canada Research Station, Harrow, Ontario, N0R 1G0. Plant Dis. 68:536, 1984. Accepted for publication 5 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-536e.

For several years we have ascribed the common powdery mildew on glasshouse and field cucumbers (Cucumis sativus L.) in southwestern Ontario to Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll. on the sole basis of asexual characters, but in November 1983, colonies of powdery mildew typical to the area and severely affecting glasshouse cucumber cultivars Harliton Seedless, Burpee Hybrid, Highmark II, and Marketmore at the Harrow Research Station had abundant cleistothecia that accorded with S. fuliginea.  This is the first record of the telemorph of S. fuliginea on cucumber in Ontario.  The observation followed 3 mo with 14.4% more sunshine hours than the 65-yr average of 436 hr; supplementary lighting was used throughout for 14 hr daily.  We have no experimental data on the effect of light.  Temperature was controlled to a minimum of 21 C.