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Development of Myrothecium Leaf Spot of Dieffenbachia maculata ‘Perfection’ at Various Temperatures. A. R. Chase, Associate Professor of Plant Pathology, IFAS, University of Florida, Agricultural Research Center, Apopka 32703. R. T. Poole, Professor of Ornamental Horticulture, IFAS, University of Florida, Agricultural Research Center, Apopka 32703. Plant Dis. 68:488-490. Accepted for publication 9 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-488.

The influence of temperature on development of Myrothecium leaf spot was tested on the foliage plant Dieffenbachia maculata ‘Perfection’ in the greenhouse and in growth chambers with temperatures between 16–33 C and 18–32 C, respectively. Temperatures along a greenhouse bench varied as much as four degrees from the pad end to the fan end. The number of leaf spots was highest near the pads, where temperatures were the lowest. Depending on the time of year, incidence of leaf spot varied as much as 200%. In growth chambers, the optimum temperature range for disease development was 21–27 C, with temperatures of 30 C or higher inhibitory to lesion formation. Plants grown at 32 C for 4 hr/day and at 24 C for 20 hr/day failed to develop lesions in most trials. In vitro optimum growth of the pathogen occurred at 28 C, with good growth also at 32 C.

Keyword(s): Myrothecium roridum.