Location: Southern Horticultural ResearchTitle: Spread potential of binucleate Rhizoctonia from nursery propagation floors to trays containing azalea stem cuttings and sanitary control options
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2014
Publication Date: 6/1/2015
Citation: Copes, W.E. 2015. Spread potential of binucleate Rhizoctonia from nursery propagation floors to trays containing azalea stem cuttings and sanitary control options. Plant Disease. 99:842-847.
Interpretive Summary: Binucleate Rhizoctonia fungi cause web blight on azaleas and other woody ornamental plants. This research focused on one aspect of how the pathogen may spread from contaminated floors of propagation houses into trays containing clean azalea stem cuttings that generate new root systems. Rhizoctonia was recovered on average from 14% of floor surfaces. The pathogen naturally declined to a smaller population level over the 6 weeks houses were empty between crops. If floor surfaces are cleaned of organic matter, the risk of the pathogen growing from the floor into rooting trays appears low. Disinfestants can eliminate the pathogen on ground fabric floors. On gravel floors, disinfestants cause a significant decrease but may not eliminate the pathogen. Combined with other sanitation methods the prospective looks favorable for producing azaleas free of binucleate Rhizoctonia. This information will benefit cooperative extension specialists and businesses that produce azaleas and other woody ornamental plants that get Rhizoctonia web blight.
Technical Abstract: Binucelate Rhizoctonia sp. (BNR), the cause of web blight, can be spread on azalea stem cuttings into propagation houses, but can be eliminated from stems by submerging cuttings in 50°C water for 21 minutes. The overall objective was to evaluate risk of rooting cuttings in trays becoming contaminated from inoculum on polypropylene fabric and gravel floors. Three separate experiments were done in 2011 and 2012 to evaluate recovery of BNR from polyethylene fabric and gravel floors in commercial propagation houses, survival of BNR over 6 weeks under fallow conditions, and the potential for growth of BNR from floors into propagation trays. A fourth study was done in 2013 and 2014 to evaluate sanitation methods and chemicals on floor materials. In experiment one, 1-27% samples were positive for BNR from floor areas. In experiment two, BNR survival was higher under 70% shade than full sun, with presence than absence of organic media, and on gravel than on fabric. In experiment three in both years, BNR was never recovered from peat in trays. In experiment four, disinfestants greatly reduced but did not totally eliminate BNR. If floor surfaces are clean of organic matter, the risk of rooting trays becoming contaminated appears low.