CAUSES OF PYTHIUM DISEASES OF ZOYSIA GREEN AND ITS CONTROL BY CHEMICALS

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Two diseases named Pythium-Spring Dead Spot and Fuzoroi-sho which occur on golf greens of manila grass(Zoysia matrella) during spring season in southern part of Japan. Pythium-Spring Dead Spot appears before or at the same time when grasses sprout whereas Fuzoroi-sho appears the patch just after sprout. Both diseases have been considered to be caused by certain physiological factors unfavorable to the initiation of growth under low temperature circumstance, because fungicides ever examined were not effective in controlling these diseases. In this study, however, we clearly demonstrated that both diseases are caused by fungal pathogens. Control of these diseases by chemicals was also successful. The results obtained are summarized as follows: (1) Pythium-Spring Dead Spot: Three kinds of Fusarium spp. were mainly isolated from grass tissues in late fall and Pythium spp. were isolated in middle spring. Two kinds of Fusarium spp. were highly pathogenic to the seedlings of Zoysia japonica. … More In the previous study, it was demonstrated that Pythium graminicola(Pg) and P.vanterpoolii(Pv) were pathogenic to seedlings of Zoysia japonica. Treatments of the green by the combination of benomyl at fall and metalaxyl hydroxyisoxazole mixture at spring were remarkably effective to protect turf surface from the damage. The influence of physical properties of soil on the occurrence of Pythium-Spring Dead spot was also investigated. As a result of discrimibant analysis by quantification scaling type 2, it was supposed that this disease was promoted to occur under the soil condition of the poor air and water permeability. (2) Fuzoroi-sho : P.graminicola(Pg), P.torulosum(Pt) and P.vanterpoolii(Pv) were mainly isolated from grass tissues and rhizosphere in the early spring. lnoculation test using seedlings of Zoysia japonica indicated that Pg and Pv were pathogenic under low temperature condition, while Pt had no pathogenicity. Treatments of the green by fungicides containing metalaxyl or hydroxyisoxazole-metalaxyl mixture in the early spring were remarkably effective to protect the turf surface from the damage. Less