ARS | Publication request: Propagating azalea stem cuttings free of binculeate Rhizoctonia spp

Submitted to: National IPM Symposium
Publication Type: Abstract Only
Publication Acceptance Date: January 13, 2012
Publication Date: June 12, 2012
Citation: Copes, W.E., Blythe, E.K. 2012. Propagating azalea stem cuttings free of binculeate Rhizoctonia spp. National IPM Symposium. 7:89.

Technical Abstract: Azalea web blight, caused by binucleate species of Rhizoctonia (BNR), occurs yearly on some azalea cultivars during nursery production in the U.S. Azalea shoots collected for cutting propagation can harbor the pathogen, thus allowing the disease to be perpetuated. Previous studies have demonstrated that submerging Rhizoctonia-infested azalea stem pieces in 50°C water for 21 minutes eliminates the pathogen and that hot water treatment did not adversely affect root development of twelve commonly grown azalea cultivars. However, subsequent contamination may occur in propagation houses. Polyethylene fabric and gravel floors were sampled in commercial nurseries one week after the previous season’s rooted cuttings were removed. BNR were recovered from 1 to 9 of 96 swabs per floor in five propagation houses. Propagation houses are usually left empty for 6 weeks before being filled with trays of the current year’s stem cuttings. When fabric and gravel infested with BNR were placed in direct sun or under 70% shade, recovery of BNR declined to 4 and 25%, respectively, over 6 weeks. When infested fabric and gravel substrates were placed beside and under trays of rooting stem cuttings for 3 months, the peat media in trays was not colonized by BNR fungi. Although BNR fungi can infest azalea stem cuttings and floors of propagation houses in nurseries, hot water treatment of stem cuttings is recommended, whereas sanitation of floors is only suggested. Further studies are in progress to develop a comprehensive integrated program to produce azalea plants free of BNR fungi.