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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research » Research » Publications at this Location » Publication #226864

Title: Effect of Plant Spacing on Microclimate and Rhizoctonia Web Blight Development in Container Grown Azalea

item Copes, Warren

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2004
Publication Date: 2/16/2005
Citation: Copes, W.E., Scherm, H. 2005. Effect of Plant Spacing on Microclimate and Rhizoctonia Web Blight Development in Container Grown Azalea. Southern Nursery Association Research Conference. 49:247-249.

Interpretive Summary: The principal cultural practice used to control Rhizoctonia web blight of azalea in commercial nurseries is to space plants so air flow will minimize humidity thus decrease disease levels, yet the benefit from spacing has never been experimentally proven. Disease, temperature, and moisture conditions were measured in 'Gumpo White' azalea plants that had been spaced at five distances from 0 to 10 inches. We determined that wider plant spacing increased evaporation, but humidity and leaf wetness was not affected enough to decrease disease severity, therefore narrower spacing could be used to increase production and revenues. The research will be beneficial to scientists, extension agents, and ornamental plant products.

Technical Abstract: Rhizoctonia web blight is a reoccurring problem in compact varieties of container-grown azalea (Rhododendron sp.) in the Gulf Coast States. During the summers of 2002 and 2003, disease severity was measured weekly in the inoculated center plant of plots consisting of 49 ‘Gumpo’ azalea plants. Plant spacing within plots was set at 0, 6, 12, 18, or 24 cm, and plots were arranged in three randomized complete blocks. Evaporative potential (EP), leaf wetness (LW), relative humidity (RH), and temperature were monitored in each plot. EP increased significantly with plant spacing, but LW, RH, and temperature, summarized to reflect environmental requirements of R. solani, were not significantly different among treatments. Plant spacing also had no significant effect on disease severity in the 2 years. Disease increased steadily from mid-July to late August or early September, then decreased. In southern Mississippi, periods conducive for web blight appear to exist weekly during most of the summer. Daily irrigation and compact plant form likely contributed to the lack of effect of spacing on disease development.