Location: Southern Horticultural ResearchTitle: Azalea Web Blight Control: Fungicide Timing in the Nursery and Hot Water Treatment of Stem Cuttings) Author
Submitted to: Extension Publications
Publication Type: Proceedings
Publication Acceptance Date: 10/8/2009
Publication Date: 10/8/2009
Citation: Copes, W.E., Hagan, A., Olive, J., Blythe, E. 2009. Azalea Web Blight Control: Fungicide Timing in the Nursery and Hot Water Treatment of Stem Cuttings. Extension Publications. 36:11. 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. Multiple control strategies are being investigated to control the fungal pathogen that causes web blight. Simple scouting methods are being used to detect the disease at an early stage so fungicides can be applied prior to the occurrence of severe crop damage. Also, the pathogen is spread on healthy-appearing, new stem growth collected for vegetative propagation, since the fungus cannot be seen by the human eye. The fungus is effectively eliminated by submerging azalea stem cuttings in 122°F water for 21 minutes. The hot water treatment was shown to be safe to stem cuttings of twelve azalea cultivars, but could cause 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: Azalea web blight is an annual problem on some evergreen azalea cultivars grown in containerized nursery production in the southern and eastern United States. Multiple control strategies are being investigated to control the binucleate Rhizoctonia species that cause web blight. The disease will develop annually, although development is faster when rainy periods occur during early summer. Simple scouting methods are showing promise for early detection of disease so fungicides can be applied prior to the development of severe crop damage. We have shown that the pathogen inhabits healthy appearing new shoot growth harvested for propagation, but the pathogen can be eliminated by submersing stem cuttings in 122°F (50°C) water for 21 minute. When stem cuttings were submerged in 122°F (50°C) water for 20 minutes, 11 of the 12 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’) rooted well. ‘Fashion’ had slightly less root growth, but root systems were healthy and likely would have achieved comparable growth within a few weeks. When stem cuttings were submerged in 122°F water for 40, 60, and 80 minute, which is longer than needed to kill the pathogen, cultivars varied in sensitivity to damage from no damage to death of the cutting.