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Disease Note

First Report of Uncinula necator Cleistothecia on Grapevines in Australia. T. J. Wicks and P. Magarey, Department of Agriculture, South Australia 5001, and R. W. Emmett, Department of Agriculture, Irymple. Victoria 3498. Plant Disease 69:727. 1985. Accepted for publication 18 March 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-727d.

Cleistothecia of Uncinula necator (Schw.) Burr are reported for the first time on Vitis vinifera L. in Australia.  They were found during late April and early May 1984 on 28 cultivars in the main grape-growing areas of southeastern Australia.  Large numbers of cleistothecia were often observed on infected leaves and terminal shoots.  On the cultivar Cardinal, for example, more than 600/cm2 were observed on terminal shoots and up to 400/cm2 on leaves.  Grape powdery mildew appears to have been present in Australia since 1866.  Since cleistothecia are visible to the naked eye, abundant development before 1984 is not likely to have been overlooked.  Reasons for their sudden appearance are obscure, but one possible explanation is that an opposite mating strain of U. necator, necessary for production of cleistothecia, was recently introduced into southeastern Australia.