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Disease Note.

First Report of Powdery Mildew on Carnation in California. G. S. Saenz, Department of Plant Biology, University of California, Berkeley 94720.. S. T. Koike, S. A. Tjosvold, and I. D. Greene, University of California Cooperative Extension, Salinas 93901. Plant Dis. 79:320. Accepted 19 .January 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0320A.

In the summer months of 1994, commercially produced cutflower carnation (Dianthus caryophyllus L.) was found to be infected by a powdery mildew in Monterey County, California. Disease surveys indicated that powdery mildew was present in at least 5 different nurseries in the county. Not all cultivars surveyed were infected. The most commonly infected cultivars were Cerise, Vanessa, President, and Katia. Mycelia were found primarily on the calyces and floral bracts and at the junction of stem nodes and leaf bases. Growth was effuse to dense, and was amphigenous. Conidiophores were straight. Foot cells were cylindric, sometimes flexuous, 28-37 μ in length, followed by two slightly shorter cells, 16-28 μ in length. Hyphal appressoria were nipple-shaped to lobed. Conidia were cylindric, produced singly, and measured 3442 x1416 μ. No fibrosin bodies were observed. Germ lubes were produced from the ends of the conidia, but no appressoria were formed. Cleistothecia were not present. The fungus was identified as Oidium dianthi Jacz (1,2). This is the first report of this disease on carnation in California.

References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) W. B. Mercer. J. Royal Hortic. Soc 41:227. 1915.