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United States Department of Agriculture

Agricultural Research Service


item Copes, Warren
item Scherm, Harald

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2005
Publication Date: 8/1/2005
Citation: Copes, W.E., Scherm, H. 2005. Plant spacing effects on microclimate and rhizoctonia web blight development in container-grown azalea. Hortscience. 40:1408-1412.

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. Drs. Copes and Scherm 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 change control recommendations used by extension agents and ornamental plant producers and provide new information to be considered by scientists.

Technical Abstract: Rhizoctonia web blight is an annual problem in compact varieties of container-grown azalea (Rhododendron spp.) in the Gulf Coast states. During the summers of 2002 and 2003, disease severity was measured weekly in 'Gumpo White' azalea plants that had been spaced at 0, 6, 12, 18, or 24 cm. Evaporation, leaf wetness, relative humidity, and temperature were monitored in each plot. Disease severity increased steadily from mid-July to late August or early September, then decreased. Evaporation increased significantly with plant spacing, but leaf wetness, relative humidity, and temperature, summarized to reflect environmental requirements of Rhizoctonia solani, were not significantly different among treatments (P > 0.05). Plant spacing also had no significant effect on disease severity. Daily irrigation and compact plant form likely contributed to the lack of effect of spacing on disease development.

Last Modified: 06/26/2017
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