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United States Department of Agriculture

Agricultural Research Service

Research Project: Production Management Research For Horticultural Crops in the Gulf South

Location: Southern Horticultural Research

Title: Rhizoctonia web blight on azalea

Author
item Copes, Warren

Submitted to: Mississippi Nursery and Landscape Association
Publication Type: Trade Journal
Publication Acceptance Date: November 1, 2009
Publication Date: January 3, 2010
Repository URL: http://www.msnla.org
Citation: Copes, W.E. 2010. Rhizoctonia web blight on azalea. Mississippi Nursery and Landscape Association, winter 2010, pg 8,23.

Interpretive Summary: Azalea web blight is an annual problem on some evergreen azalea cultivars grown in containerized nursery production in the southern and eastern United States. Fungicides minimize plant damage but do not prevent spread. Simple scouting methods are being tested to detect initial disease stages in early summer and improve timing of fungicides. Since the fungal pathogen is spread on healthy-appearing, new stem growth collected for vegetative propagation in the spring, multiple control strategies are being investigated. The fungus can be eliminated from stems by submerging azalea stem cuttings in 122°F water for 21 minutes. The hot water treatment was safe to stem cuttings of twelve azalea cultivars, but caused minor to severe damage if stem cuttings were unintentionally submerged for 40 to 80 minutes. The information will be beneficial to research and extension scientists and commercial ornamental plant producers.

Technical Abstract: Currently, fungicides are the only useful control for azalea web blight, but fungicides do not eliminate the pathogen. We have discovered that Rhizoctonia colonizes the entire azalea plant 12 months of the year in the Gulf Coast climate. This results in healthy appearing stems collected for propagation being infested with Rhizoctonia and contributes to next year’s crop being infested. One possible control approach is production of azaleas free of the Rhizoctonia fungi that cause web blight. Controls used in field crops (e.g. crop rotation, deep-plowing, etc.) are impractical in azalea production. Submerging stem cuttings in 122°F water for 21 minutes eliminates Rhizoctonia from stem cuttings while disinfestants and fungicides do not. Twelve cultivars rooted well after receiving a 20 minute hot water treatment, so the treatment appears to be safe. The next steps in this control concept is to verify that the vast majority of plants can be kept free of the pathogen throughout the entire production cycle; in other words, clean cuttings do not become infested in the propagation house and clean plants do not become infested on the nursery. This is a new control strategy that may open the possibility to control diseases for which we currently have no real control capability.

Last Modified: 10/1/2014
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