Powdery Mildew of Greenhouse Cucumbers and Tomatoes Caused by Leveillula taurica in Idaho. R. L. Forster, Plant Pathology Division, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Kimberly 83341. . Plant Dis. 73:1020. Accepted for publication 24 July 89. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-1020B.
In May 1988, powdery mildew caused by Leveillula laurica (Lev.) Arn. (anamorph: Oidiopsis taurica (Lev.) Salmon) was found infecting cucumbers (Cucumis sativus L. 'Corona' and 'Farbio,) and tomatoes (Lycopersicon esculentum Mill. 'Laura') growing in a greenhouse in Minidoka County, Idaho. No cleistothecia were observed, and Erysiphe or Sphaerotheca spp. were not detected. Symptoms on cucumber leaves were white, angular lesions consisting of conidia and conidiophores of tbe patbogen on abaxial surfaces and corresponding chlorotic to necrotic lesions on adaxial surfaces. Symptoms on tomato leaves were yellow spots with small necrotic flecks near the centers. Ultimately, extensive leaf necrosis developed in both hosts. Sporulation was profuse on cucumber and sparse on tomato. Dimorphic conidia (pyriform and cylindrical), 58-81 X 15-19 µm, were produced on abaxial and adaxial surfaces in both hosts. Identity of the pathogen was confirmed microscopically by S. V. Thomson at Utah State University. Infected tomato transplants from Utah growing near the greenhouse are the suspected source of the pathogen. This is the first report of this pathogen infecting cucumbers in North America and the first report of the pathogen in Idaho.