Location: Southern Horticultural ResearchTitle: Rhizoctonia web blight Author
Submitted to: American Phytopathological Society Press
Publication Type: Book / Chapter
Publication Acceptance Date: 6/28/2012
Publication Date: 6/1/2014
Citation: Copes, W.E., Benson, M.D. 2014. Rhizoctonia web blight. American Phytopathological Society Press. p. 15-19. Interpretive Summary: Rhizoctonia web blight is an annual disease problem of evergreen azaleas and other ornamental plants in ornamental plant nurseries. The only effective disease control method available is application of fungicides. This treatise provides a summary of biological information important for development of web blight control strategies. The current status of knowledge is given about timing fungicide application to prevent severe blight symptoms and about cultural management practices being evaluated to eliminate the pathogen and produce a healthier azalea crop. Rhizoctonia web blight control will benefit production of other ornamental plant genera, such as holly, that also get web blight. The information will be directly useful to extension specialists and crop advisors, as well as ornamental plant production managers.
Technical Abstract: Rhizoctonia web blight, caused by several Rhizoctonia spp., is an important disease of evergreen azaleas and other ornamental plants in nurseries. The primary pathogens causing web blight are binucleate Rhizoctonia anastomosis groups (AG) (= Ceratobasidium D.P. Rogers, teleomorph). In southern AL and MS, BNR can be recovered from all depths of the growing medium and from entire lengths of stems in the plant’s canopy during 12 months of a year. The main symptom of web blight is individual dead leaves. Web blight symptoms first appear during early summer on random plants across blocks of uniform azalea cultivars in the nursery and become severe in July and August. Currently, the main spread mechanism appears to be infested stem cuttings used for vegetative propagation of following year’s azalea crop. Two to three well timed fungicide applications at 14-21-day intervals at labeled rates will effectively suppress disease symptom progression most years. The initial fungicide application should be made to the more susceptible cultivars, such as azalea ‘Gumpo’, about July 8 in southern AL and MS. Due to year-to-year differences in disease progress, scouting will allow more precise timing. The treatise provides a comprehensive summary of azalea web blight and an advanced discussion of disease control methods.