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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research » Research » Publications at this Location » Publication #300285

Title: Sanitation Can Be A Foundation Disease Management Tool: Potential Of Spreading Binucleate Rhizoctonia from Nursery Propagation Floors To Trays Containing Azalea Stem Cuttings

Author
item Copes, Warren

Submitted to: International Plant Propagators Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/5/2013
Publication Date: 8/1/2014
Citation: Copes, W.E. 2014. Sanitation Can Be A Foundation Disease Management Tool: Potential Of Spreading Binucleate Rhizoctonia from Nursery Propagation Floors To Trays Containing Azalea Stem Cuttings. International Plant Propagators Proceedings. 63:475-477.

Interpretive Summary: Binucelate Rhizoctonia spp., the cause of web blight, are present all year on container-grown azaleas in the southern U.S, including on stem cuttings used to propagate azalea. The fungal pathogen can be eliminated from vegetative stem cuttings by submerging them in 50°C water for 21 minutes. The objective of this research was to evaluate the risk of pathogen-free stem cuttings becoming infected from contaminated polypropylene fabric and gravel floors in propagation houses. Three experiments were done in 2011 and repeated in 2012. In experiment one, fabric and gravel floors were tested for the presence of Rhizoctonia. Up to 9% of 96 samples per cultivar were positive for the pathogen. In experiment two, fabric and gravel floor material was inoculated and Rhizoctonia survival evaluated over 6 weeks. Rhizoctonia recovery declined 75% under shade and 86-96% under full sun. In experiment three, hot water treated azalea stem cuttings were stuck in peat trays that were set on or beside inoculated pieces of fabric and gravel floor material and maintained under a misting regime for 12 weeks. In both years, Rhizoctonia was not recovered from peat in trays of rooted stem cuttings. If floor surfaces are clean of organic matter, the risk of rooting trays becoming contaminated appear low. The information will be useful to Extension Personnel working with commercial nursery producers and will help producers consider implementing radical web blight reduction.

Technical Abstract: Binucelate Rhizoctonia spp. (BNR), the cause of web blight, are present all year on container-grown azaleas in the southern U.S. BNR can be eliminated during vegetative propagation by submerging stem cuttings in 50°C water for 21 minutes. The objective was to evaluate risk of rooting trays being contaminated from inoculum on polypropylene fabric and gravel floors in propagation houses. Three experiments were done in 2011 and repeated in 2012. In experiment one, floors of commercial propagation houses were swab sampled on a grid pattern and sponges plated on Ko and Hora agar. 1-9% of 96 samples per cultivar were positive for BNR from fabric and gravel floors. In experiment two, samples of fabric and gravel inoculated with BNR were set under 70% shade and full sun, with and without interval timed irrigation, for six weeks. BNR recovery declined 75% under shade and 86-96% under full sun. In experiment three, trays with hot water treated azalea stem cuttings stuck in peat mixtures were set on or beside inoculated pieces of fabric and gravel and maintained under a misting regime for 12 weeks. In both years, BNR was not recovered from peat in trays of rooted stem cuttings even though BNR was recovered from 60-94% of the inoculated substrates at the end of 12 weeks. BNR persists on fabric and gravel floors but declines over the 6 weeks houses are empty. If floor surfaces are clean of organic matter, the risk of rooting trays becoming contaminated appear low.