Disease Note.

Occurrence of Powdery Mildew (Erysiphe sp.) on Greenhouse Tomatoes in Canada. R. R. Belanger, Departement de Phytologie, Universite Laval, Quebec, PQ G1K 7P4 Canada. W. R. Jarvis, Agriculture Canada, Research Station Harrow, ON NOR 1 GO Canada. Plant Dis. 78:640. Accepted for publication 22 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0640E.

In fall 1993, powdery mildew was reported simultaneously on greenhouse tomatoes (Lycopersicon esculentum Mill.) in three separate locations in the province of Quebec, Canada. The pathogen was observed on cvs. Capello and Trust from the areas of Montreal, Quebec City, and Lac St-.lean, each geographically separated by at least 250 km (150 miles). White powdery mildew pustules developed on the upper surface of the leaf and were more frequent on mature than on young leaves. Individual lesions were somewhat circular but sometimes merged to cover large areas of the leaf surface. Cleistothecia were absent. Development of the disease was confined lo certain areas within each greenhouse but was extensive enough to have warranted chemical control had any been registered. Artificial inoculations on healthy tomato plants produced typical signs of the disease. On the basis of conidial characters, the fungus was identified as Erysiphe sp., either E. orontii Cast or E. cichoracearum DC. It clearly differed from Leveillula taurica, another common powdery mildew on tomato prevalent in warmer countries. It was similar to the European fungus described by Fletcher et al (1) and Vakalounakis and Papadakis (2) as Erysiphe sp. This is the first report of Erysiphe on mature tomato plants in North America.