The effect of soil fungicide treatments on the inoculum potentials of spermosphere fungi and damping-off

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Abstract
Turnip seeds were used to measure changes in inoculum potentials of spermosphere fungi following soil fungicide applications and invasion of treated soils by these fungi in the field. The normal spermosphere mycofiora of untreated soil was found to be dominated by Fusarium and Pythium spp. A good correlation between spermosphere inoculum potentials of Fusarium, Pythium spp., and Rhizoctonia solani and damping-off in infested soil in both field and glass-house was established. Captan and calomel in the field at 100 p.p.m. and 500 p.p.m. were highly effective in controlling damping-off fungi. PCNB controlled only R. solani, and copper oxychloride was ineffective. “Lanstan” gave initially good control but treated soil was rapidly invaded in the field. High spermosphere inoculum potentials of Penicillium, Trichoderma, and Actinomyces spp., which followed some of the treatments, were always associated with low inoculum potentials of damping-off fungi.