Ecology of Green Algae in Paddy Fields and Their Control with Chemicals

概要

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Lowland paddy fields become frequently infested with several kind of green algae soon after the transplanting of rice plants, and occasionally they bring about the unexpected damage to rice plants. This studies were carried out to make clear the ecology of these green algae, especially Hydrodactyon reticulatum and Spirogyra communis, and additionally to establish the method of their control with chemicals. The results obtained are as follows.(1) Green algae in paddy fields were classified three types viz. unicellular, colonial and filamentous type. Of these, Hydrodactyon reticulatum as colonial type and Ulothrix aequalis as filamentous type were the most injurious to rice plants.(2) In paddy fields, emergence of Spirogyra communis and Ulothrix aequalis was two or three times a year, and Hydrodactyon reticulatum once or two times.(3) Nitrogen and phosphoric acid were indispensable to the growth and multiplication of Hydrodactyon reticulatum, especially phosphoric acid to the multiplication.(4) Water-and soil-temperature went down as the increase of colonies, and as the results emergence of tillers of rice plants was inhibited.(5) Several herbicides useful as an algicide were found through the screening test.
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