Effects of Chlorpyrifos and Pythium splendens on Growth of Rex Begonia. L. S. Osborne, Associate Professor of Entomology, University of Florida, IFAS, Agricultural Research and Education Center, 2807 Binion Road, Apopka 32703. A. R. Chase, Associate Professor of Plant Pathology, University of Florida, IFAS, Agricultural Research and Education Center, 2807 Binion Road, Apopka 32703. Plant Dis. 71:525-527. Accepted for publication 16 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0525.

Incorporating granular chlorpyrifos (7.42 g a.i./m³) or drenching with an equivalent amount of a wettable powder formulation significantly reduced growth of Begonia × rex-cultorum. Untreated plants inoculated with Pythium splendens were smaller than control plants. When plants were treated with chlorpyrifos and inoculated with P. splendens, an interaction between these two factors resulted in a significantly synergistic reduction in plant growth. Importance of the interaction was influenced by formulation and rate of chlorpyrifos used. Stunting caused by this interaction was reduced when plants were treated with metalaxyl, which is effective in controlling Pythium root rot.