Potential for the integration of biological and chemical control of sheath blight disease caused by Rhizoctonia solani on rice

Biological control using antagonistic microbes to minimize the use of chemical pesticides has recently become more prevalent. In an attempt to find an integrated control system for sheath blight, caused by Rhizoctonia solani in rice, Streptomyces philanthi RM-1-138, commercial formulations of Bacillus subtilis as Larminar^® and B. subtilis strain NSRS 89-24+MK-007 as Biobest^® and chemical fungicides including carbendazim^®, validamycin^®, propiconazole^® and mancozeb^® were applied alone and in combination with S. philanthi RM-1-138. In vitro experiments showed that all treatments tested did provide some control against mycelial growth and sclerotia production by R. solani PTRRS-9. In addition, the four chemical fungicides had no detrimental effects on S. philanthi RM-1-138 even at high concentrations (up to 100 μg/ml). The efficacy of S. philanthi RM-1-138, the commercial formulations of B. subtilis, chemical fungicides alone or in combination with S. philanthi RM-1-138 was also tested in a greenhouse experiment against sheath blight disease on rice plants. All treatments showed some protection of rice for sheath blight by 47–60 % when carbendazim^® was applied alone and up to 74 % when combined with S. philanthi RM-1-138.