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Cercospora omphakodes Infection and Disease Development in Phlox divaricata. R. W. Judd Jr., Graduate Assistant, Department of Plant Pathology, Rutgers University, New Brunswick, New Jersey 08903, Present address of senior author: 322 North Main Street, Wallingford, Connecticut 06492; J. L. Peterson, Professor, Department of Plant Pathology, Rutgers University, New Brunswick, New Jersey 08903. Phytopathology 64:1108-1111. Accepted for publication 14 March 1974. DOI: 10.1094/Phyto-64-1108.

Cercospora omphakodes causes a leaf spot on Phlox divaricata in New Jersey. Infectivity was tested under nine light intensities and three temp. Infection was greatest under 1.72 × 10⁴ lux and at 26 and 32 C. Disease development after infection was observed under six light intensities and two temp. The most rapid and severe development occurred under 3.23 × 10⁴ lux and at 32 C. The pathogen enters the host through open stomata, never penetrating directly through the epidermis. The fungus overwintered in infected leaves on the host plant, surviving temp of –20 C. In carbon and nitrogen nutrition studies in liquid shake culture, the organism grew best on fructose and tryptophan, respectively. The optimum temp for growth was between 24 and 28 C.