Thermotherapy rids azaleas of deadly fungal disease

Dec 13, 2011
These are rooted cuttings of azalea "Wakaebisu" with lower leaf drop due to Rhizoctonia web blight. Credit: Photo by Warren Copes

Azalea web blight, caused by a species of the plant pathogen Rhizoctonia, occurs each year on some containerized azalea cultivars during nursery production, particularly in the southern and eastern United States. Azalea shoots can harbor the pathogen, spreading the devastating, costly disease through propagation.

Research has indicated that simply submerging terminal leafy cuttings of 'Gumpo White' azalea in 50°C water for 21 minutes eliminates binucleate Rhizoctonia species from plant tissues. Before recommending commercial use of the practice—known as " treatment" or "thermotherapy"—industry professionals needed to learn more about potential damage to evergreen azaleas resulting from the treatments. Warren E. Copes of the USDA-Agricultural Research Service (Thad Cochran Southern Horticultural Laboratory) and Eugene K. Blythe of the Coastal Research and Extension Center at Mississippi State University designed experiments to test 12 azalea cultivars for rooting response and sensitivity to a variety of hot water treatments.

Copes and Blythe used terminal cuttings of the azalea cultivars Conleb (Autumn Embers), Fashion, Formosa, Gumpo White, Hardy Gardenia, Hershey Red, Macrantha Pink, Midnight Flare, Red Ruffles, Renee Michelle, Roblel (Autumn Debutante), and Watchet. The cuttings from all 12 cultivars were collected and submerged or not submerged in 50°C water for 20 minutes before in one experiment; all cultivars tolerated the submersion test. Cuttings collected from the 12 cultivars were submerged in 50°C water for 20, 40, 60, and 80 minutes in a second experiment. "The cultivars varied in sensitivity when exposed to 50°C water for 60 to 80 minutes, resulting in differing responses in and final count", Copes said.

In a third experiment degrees of leaf damage caused by hot water submersion or by leaf removal were evaluated for the effect on root development and subsequent leaf count on rooted cuttings of 'Gumpo White' and 'Roblel'. According to the results, incremental increases in leaf damage from hot water resulted in incremental reductions in the final leaf count and extent of root development for the two cultivars, while increasing leaf removal caused no reduction until 75% or greater leaf area was removed. "Despite the risks imposed by submersing azalea cuttings, we found all 12 to be tolerant of submersion durations long enough to eliminate binucleate Rhizoctonia species from stem and leaf tissue with only a low likelihood of sustaining detrimental damage", the scientists wrote in the report published in HortScience.

Copes and Blythe concluded that hot water treatment provides an alternative and effective disease control method for eliminating Rhizoctonia from azalea cuttings. "Thermotherapy provides an example of how simple techniques may provide effective disease control when appropriately applied."

Explore further: Fall pest has many South Central Texans seeing spots before their eyes

More information: The complete study and abstract are available on the ASHS HortScience electronic journal web site: hortsci.ashspublications.org/c… ent/abstract/46/1/52

Provided by American Society for Horticultural Science

5 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

Early defoliation of Great Lakes wine grapes tested

Dec 12, 2011

Wine grape production in the Great Lakes Viticultural Region can be a challenging enterprise. Spring frost, winter injury, short and variable growing seasons, and cool, humid growing conditions subject grape ...

Does hotter mean healthier?

Feb 03, 2009

Phytophthora blight, caused by Phytophthora capsici, is a major plant disease that affects many crop species worldwide, including chile peppers in New Mexico. Farmers' observations suggested that Phytophthora capsici c ...

'Non-invasive' cultivar? Buyer beware

Oct 07, 2011

Cultivars of popular ornamental woody plants that are being sold in the United States as non-invasive are probably anything but, according to an analysis by botanical researchers published in the October issue of BioScience. Tiffan ...

Recommended for you

Wildlife groups seek help for California owl

16 hours ago

Loggers cutting down forests burned in wildfires could bring about the extinction of California spotted owls, wildlife advocates said Tuesday as they sought protection for the birds under the federal Endangered ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.