The present paper deals with the results of experiments on the effects of some herbicides on the occurence of Helminthosporiose of rice plants from the chemotherapeutic view point.
Sodium 2, 4-D, sodium PCP and sodium MCP were used in these experiments. These herbicides were supplied to the rice plants through roots. 2, 4-D and PCP decreased the occurence over 10^<-6> M solution. MCP decreased the occurence in 10^<-4> M solution, and under 10^<-5> M solution, promoted the occurence. Then, some experiments were carried out on the effects of the herbicides on the conidial germination and hyphal growth of the causal fungus in order to know the relationships between the occurence of the Helminthosporiose and fungicidal activities of the herbicides, and some discussions were given on the experimental results.