Disease Note

Powdery Mildew of Cotton Caused by Oidiopsis taurica in California. J. C. Correll, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 70:259. Accepted for publication 18 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-259d.

Small (<1.5 cm), angular, chlorotic lesions were observed on cotton (Gossypium hirsutum L. ‘Acala GC-510’) in Fresno County, California, in August 1985. Conidia and conidiophores of Oidiopsis taurica (Lév.) Salmon (= Leveillula taurica (Lév.) Arn.) were identified on both the adaxial and the abaxial surface of all lesions. Two morphologically distinct conidia were observed. Terminal conidia were pyriform, with one end tapering to a point; other conidia were more cylindrical. Pyriform and cylindrical conidia measured 65.9 × 18.5 and 57.1 × 18.0 μm, respectively. Lesions were observed late in the season and were found primarily on older foliage. Powdery mildew was found in only one field; incidence was low and foliar damage minimal. The teleomorph was not found. The cotton field was adjacent to and downwind of a tomato field with a very high incidence of powdery mildew caused by O. taurica. This is the first report of powdery mildew of cotton in the United States.