Spread Potential of Binucleate Rhizoctonia from Nursery Propagation Floors to Trays Containing Azalea Stem Cuttings and Sanitary Control Options

Abstract

Binucleate Rhizoctonia sp. (BNR), the cause of web blight, can be spread on azalea stem cuttings into propagation houses, but also can be eliminated from stems by submerging cuttings in 50°C water for 21 min. The overall objective was to evaluate risk of stem cuttings in trays becoming contaminated from inoculum on polypropylene fabric and gravel floors of propagation houses by evaluating four spread aspects in separate experiments. In experiment one, BNR was recovered from 1 to 50% samples from floor areas. In experiment two, BNR survival was higher under 70% shade than full sun, with the presence of organic media than its absence, and on gravel than on fabric. In experiment three in both years, BNR was never recovered from peat in trays beside or on colonized floor materials. In experiment four, disinfestants greatly reduced BNR on ground fabric and significantly on gravel. Results show BNR persists in propagation houses, yet spread into propagation trays is very low. Results imply the importance of cleaning floor surfaces of organic matter. Disinfestants further reduce propagule survival, but may not completely eliminate BNR, especially on gravel.