Biological Control of Rhizoctonia and Pythium Damping-Off of Cucumber: An Integrated Approach

Binucleate Rhizoctonia spp. were evaluated singly and in combination with seed treated with selected biocontrol bacteria, fungicides, or osmopriming agents in the greenhouse and field for control of Rhizoctonia and Pythium damping-off of cucumber. In the greenhouse, in a pasteurized soil mix, treatments with 8 of 19 isolates of binucleate Rhizoctonia spp. yielded decreased (P = 0.05) levels of preemergence damping-off caused by R. solani. Osmopriming cucumber seed with KNO3, NaCl, or polyethylene glycol (PEG 8000) did not protect cucumber from Rhizoctonia and Pythium damping-off in naturally infested soil in the greenhouse. Treating cucumber seed with strain E6, ECH, and ECT of Enterobacter cloacae and sowing in soil alone or in soil amended with isolate 232-CG of binucleate Rhizoctonia sp. resulted in decreased (P = 0.05) levels of Rhizoctonia and Pythium preemergence damping-off in naturally infested soil in the greenhouse but not in the field. Amendment of isolate 232-CG to soil and combining it with seed treatment or soil application of metalaxyl produced decreased (P = 0.05) levels of Rhizoctonia and Pythium preemergence damping-off in 12 naturally infested fields at three geographic locations when compared with nontreated seed sown in soil alone or in soil amended with isolate 232-CG alone. Seed treated with metalaxyl and sown in soil amended with isolate 232-CG developed decreased (P = 0.05) levels of Rhizoctonia and Pythium preemergence damping-off at 20 and 30% of the field sites compared to seed treated with captan and metalaxyl, respectively. However, seed treated with metalaxyl or captan had higher (P = 0.05) disease incidence of Rhizoctonia at 20 and 60% of the field sites, respectively, when compared to seed treated with metalaxyl and sown in soil amended with isolate 232-CG. Control of cucumber damping-off caused by R. solani and Pythium spp. requires an integrated approach and can be achieved using the binucleate Rhizoctonia sp. isolate 232-CG combined with the fungicide metalaxyl. This treatment protected cucumber from Rhizoctonia and Pythium damping-off as effectively as the recommended fungicide captan. (C) 1991 Academic Press, Inc.