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Development of Gray Mold of Poinsettia and Powdery Mildew of Begonia and Rose Under Split Night Temperatures. B. Sammons, Former Graduate Student, Department of Botany, University of Maryland, College Park 20742. J. F. Rissler, Assistant Professor, Department of Botany; and J. B. Shanks, Professor, Department of Horticulture, University of Maryland, College Park 20742. Plant Dis. 66:776-777. Accepted for publication 30 December 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-776.

Under four different regimes of split night temperatures (10 C night minimum, 17 C day minimum) and continuous temperatures of 17 C, no significant increase in incidence of gray mold of poinsettia (caused by Botrytis cinerea) occurred and no significant change in severity of powdery mildews of rose and begonia (caused by Sphaerotheca pannosa and Erysiphe cichoracearum, respectively) occurred. At continuous 10 C, incidence of gray mold was significantly higher, severity of begonia powdery mildew was significantly lower, and severity of rose powdery mildew was unchanged compared with continuous 17 C.