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United States Department of Agriculture

Agricultural Research Service

Title: Rhizoctonia in Container Grown Azalea, and Camellia Twig Blight: Incubation and Latency Periods

Author
item Copes, Warren

Submitted to: Annual Horticulture Field Day Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 30, 2003
Publication Date: October 5, 2003
Citation: Copes, W.E. 2003. Rhizoctonia in Container Grown Azalea, and Camellia Twig Blight: Incubation and Latency Periods. Proceedings of 31th Annual Horticulture Field Day. 31:29.

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. Camellia twig blight, caused by Colletotrichum gloeosporioides, is a disease problem that commonly occurs on several Camellia species in the southern United States. To determine the potential seasonal differences in time from infection until the appearance of symptoms, stems of Camellia sasanqua ‘Rosa’ plants were artificially infected with the fungus then moved outside under overhead sprinkler irrigation, every month over two years. Twig blight symptoms developed sooner in periods with a higher number of hours between 15 – 30 ° C. The lowest and highest hazard ratios (risks of developing blight) occurred in winter and summer months, respectively. Knowing when infection occurred in relationship to the appearance of symptoms will help extension and research scientists when testing efficacy of control measures.

Technical Abstract: Rhizoctonia web blight is a reoccurring problem in compact varieties of container-grown azalea (Rhododendron sp.) in the Gulf Coast States. Disease severity was measured weekly in ‘Gumpo’ azalea plants spaced at distances of 0, 6, 12, 18, or 24 cm. 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, although disease increased steadily from mid-July to early September. Daily irrigation and compact plant form likely contributed to the lack of effect of spacing on disease development. Camellia twig blight, caused by Colletotrichum gloeosporioides, is a disease problem that commonly occurs on several Camellia species in the southern United States. To determine the potential seasonal differences in time from infection until the appearance of symptoms, stems of Camellia sasanqua ‘Rosa’ plants grown in containers were artificially infected with the fungus in a greenhouse then moved outside under overhead sprinkler irrigation, every month over two years. Continuous temperature data was recorded. Survival tended to be shorter (symptoms developed sooner) in periods with a higher number of hours between 15 – 30 ° C. The lowest and highest hazard ratios (risks of developing blight) occurred in winter and summer months, respectively. The largest overlap when symptoms first appeared occurred in May and June from stems infected from February to May. Knowing when infection occurred in relationship to the appearance of symptoms will help extension and research scientists when testing efficacy of control measures.

Last Modified: 10/1/2014
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