Integrated Control of Rhizoctonia solani Damping-Off of Radish: Effect of Successive Plantings, PCNB, and Trichoderma harzianum on Pathogen and Disease

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Abstract
When applied to soil at rates of 0.04-0.15 g/kg (dry wt basis), wheat-bran cultures of T. harzianum protected radish seedlings from damping-off induced by R. solani and increased radish germination in noninfested soils. Protection lasted for 5 successive weekly plantings. Pentachloronitrobenzene (PCNB) at 4 .mu.g/g soil (active) added with T. harzianum inoculum had an additive effect on disease control and a synergistic effect on the decrease inoculum density of R. solani propagules. In the absence of T. harzianum, PCNB alone delayed the decrease of viable R. solani propagules. At a relatively low initial inoculum density (5 propagules/g soil) when radishes were replanted every week, inoculum concentration rose during the first 3 wk. Cultures of T. harzianum added to this soil permitted no increase in inoculum density. With high inoculum levels (80 propagules/g soil) T. harzianum accelerated reduction in population of R. solani in comparison with nontreated controls. After 4 or 5 successive plantings of radish in infested, nonamended soil, incidence of Rhizoctonia damping-off decreased substantially. A conduciveness test was developed and used for quantitative evaluation of the ease with which disease increased in a given soil. Soil conduciveness declined to a minimum in the nonamended, infested treatment after 5 successive plantings. The concept of incorporating soil conduciveness (along with inoculum quality and inoculum concentration) into the capacity portion of the inoculum potential is suggested.