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Occurrence of Binucleate Rhizoctonia spp. on Azalea and Spatial Analysis of Web Blight in Container-Grown Nursery Stock. T. A. Frisina, Former Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. D. M. Benson, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 73:249-254. Accepted for publication 31 October 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0249.

Binucleate Rhizoctonia spp. were isolated from potting media, from symptomatic leaves of rooted azalea cuttings in propagation houses, and from container-grown azaleas at two nurseries in North Carolina. Thirty-one of 38 selected isolates of binucleate Rhizoctonia spp. from potting media were pathogenic on azalea. Propagule density of all Rhizoctonia spp. in potting medium in 15-cm-diameter containers of azaleas in production areas ranged from <1.0 to approximately 6.0 propagules per gram in both years of the study. The incidence of web blight in container-grown azaleas at nursery 1 in 1986 ranged from <1% on day 191 (early in the production season) to 51% on day 283. Spatial pattern of symptomatic azaleas in 1986, as determined by goodness-of-fit to discrete frequency distributions, was random at low disease incidence and became more aggregated as incidence increased. Two-dimensional distance class analysis also revealed a higher frequency of infected pairs of plants and a greater degree of clustering of diseased plants as disease incidence increased. Inoculum density of Rhizoctonia spp. in the container media and disease incidence of azaleas were not correlated.