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Control of Rhizoctonia Stem Rot of Poinsettia During Propagation with Fungicides that Prevent Colonization of Rooting Cubes by Rhizoctonia solani. D. M. Benson, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 75:394-398. Accepted for publication 17 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0394.

The effectiveness of several fungicides applied either as foliar sprays or as rooting-cube soaks was compared for control of Rhizoctonia stem rot of poinsettia during propagation. Rhizoctonia solani was introduced to the surface of rigid foam rooting cubes at the time cuttings were stuck. Benomyl at 0.3 g a.i./L, chlorothalonil at 1.8 ml a.i./L, flutolanil at 0.3 g a.i./L, iprodione at 0.6 g a.i./L, and metalaxyl + benomyl at 0.5 g a.i./L all prevented stem rot. Rooting-cube soaks of flutolanil, iprodione, and metalaxyl + benomyl were as effective as foliar sprays in disease control. Foliar sprays of quintozene at 0.45 g a.i./L and ethazole + thiophanate methyl at 0.24 g a.i./L were not as effective in control of stem rot as the other fungicides tested. Root development on cuttings treated with flutolanil and metalaxyl + benomyl was not different from the untreated, uninoculated control. Root development was intermediate with benomyl, chlorothalonil, and iprodione and poorest with quintozene and ethazole + thiophanate methyl. Untreated rooting cubes (47 cm3) were colonized by R. solani from inoculum placed on the cube surface in 25 days. Rooting cubes of poinsettia treated with metalaxyl + benomyl, flutolanil, and iprodione at 0.25 g a.i./L were not colonized as extensively as untreated cubes. Funigicide effectiveness in control of stem rot was related directly to the extent of colonization of rooting cubes by R. solani.

Keyword(s): Euphorbia pulcherrima.