Location: Southern Horticultural ResearchTitle: Chemical and Hot Water Treatments to Control Rhizoctonia on Infected Azalea Stem Cuttings Author
Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2009
Publication Date: 8/1/2009
Publication URL: http://sna.org/content/Plant%20Pathology%202009_2.pdf
Citation: Copes, W.E., Blythe, E. 2009. Chemical and Hot Water Treatments to Control Rhizoctonia on Infected Azalea Stem Cuttings. Southern Nursery Association Research Conference 54:63-65. Interpretive Summary: The fungal pathogen, binucleate Rhizoctonia species, cause azalea web blight during the summer. The fungus can grow along stems and reach new shoot growth of azalea ‘Gumpo White’ during the spring. The healthy appearing stem cuttings are used for propagation, but result in spread of the pathogen into plant propagation houses. Chemical treatments with disinfestants or fungicides did not eliminate the pathogen from stems. Submerging the stems in 122 °F for 21 minutes eliminated the pathogen while causing only minor damage to the leaves. Cooler water temperatures did not eliminate the pathogen and hotter water temperatures caused severe plant damage. This information provides a method to produce pathogen-free cuttings and could be useful to commercial nurseries that produce azaleas and extension scientists.
Technical Abstract: Spring shoot growth of azalea 'Gumpo White' used for propagation of stem cuttings can harbor binucleate Rhizoctonia species that cause web blight, thus the pathogen is unsuspectingly propagated with the plant. The objective of this study was to evaluate efficacy of disinfesting methods (commercially available disinfestants, fungicides, and hot water) for eliminating Rhizoctonia from azalea stems without damaging plant tissue. Several rates of disinfestants (sodium hypochlorite, hydrogen dioxide, quaternary ammonium chloride) and fungicides (chlorothalonil plus thiophanate methyl, and flutolanil) did not eliminate Rhizoctonia from stem cuttings. However, recovery of Rhizoctonia was eliminated by submersing stems in 122 °F (50 °C) water for 21 minutes and in 131 °F (55 °C) water for 5 minutes, which only minor damage to leaves. Severe leaf damage resulted when stems were submersed in 131° C water for > 12 minutes and at water temperatures > 133 °C for even shorter time durations. The margin of error in time between killing the pathogen and severely damaging plant tissue is narrower at 131 °C than at 122° F, thus Rhizoctonia elimination is more safely achieved by submerging stems in 122° C water for 21 minutes.