A Leaf Spot of Florists' Geranium Incited by Pseudomonas cichorii. Arthur W. Engelhard, Professor of Plant Pathology, IFAS, University of Florida, Agricultural Research and Education Center, Bradenton 33508-9324. H. C. Mellinger, Glades Crop Care, Ft. Myers, FL 33901, R. C. Ploetz, Graduate Assistant in Plant Pathology, IFAS, University of Florida, Gainesville 32611, and J. W. Miller, Florida Department of Agriculture & Consumer Services, Division of Plant Industry, Gainesville 32602. Plant Dis. 67:541-544. Accepted for publication 7 December 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-541.

A new bacterial disease characterized by spots on the leaf, petiole, flower, and peduncle of the florists' geranium (Pelargonium × hortorum) was shown to be incited by Pseudomonas cichorii. An isolate from geranium was pathogenic to cabbage (Brassica oleracea var. capitata), cauliflower (B. oleracea), chrysanthemum (Chrysanthemum morifolium), and a weed host, prickly poppy (Argemone mexicana). The causal organism produced a green fluorescent pigment on King's medium B and was arginine dihydrolase negative and oxidase positive, which identified it as P. cichorii. In greenhouse experiments, cupric hydroxide, cupric hydroxide with sulfur, and basic copper sulfate, when used singly or in combination with mancozeb, were moderately effective in controlling Pseudomonas leaf spot on P. × hortorum cultivars Heidi and Ringo plants.

Keyword(s): Pseudomonas erodii.