The present paper is reported on the change of fungal flora in soil caused spring dead spot disease of Zoysia at Ibaragi Country Club extending over 1975 and 1977.
The number of microorganisms, especially fungi and actinomycetes, in turf was less than in field. There was no difference about the fungal number on dedris between in diseased soil and in healthy soil, but was difference with composition of fungal flora; i. e., the flora became more simply in diseased soil.
The fungal flora in wettable soil was more simply than in dried, too, and the number of Phycomycetes increased in former. From the succession of fungi on roots and subterranean stems of Zoysia it was appeared that
Fusarium roseum, Pythium spp. and
Rhizoctonia solani infected turfgrass in autumn already, and
Curvularia, F. oxysporum and
Trichoderma grew on turf grass as saprophytes. These six fungi had their activities in high temperature and in low temperature they lost their activities in order to
Pythium, Fusarium, Rhizoctonia, Trichoderma and
Curvularia.
Certainly they decreased in winter temporarily and increased in spring again, but the ratio of increase was more gently in pathogens than in saprophytes.
From these results it is considered that the pathogen caused Zoysia spring dead spot may be
Pythium spp.,
F. roseum or
R. solani that have weak pathogenicity, therefore, they invade into turfgrasses in autumn when the hosts begin to depreciate their activities. The infection may be accomplished as complex infection by other pathogens and saprophytes such like
Curvularia etc. in autumn, but the development of disease may be difficult in next warm season because of saprophytic competitions with other fungi like as
Trichoderma and recovery of host activities.
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