WHY DOES CYPERUS FLACCIDUS R. BR. INFEST THE RICE FIELD IN JAPAN?

摘要

Recently, it was reported that C. flaccidus R. Br. infested the paddy rice field and caused the loss of rice yield. These prompted us to clarify the germination characteristic, ecology and mechanism of the distribution of C. flaccidus. We reported that the germination rate was highest at 20°C and light was necessary to the seed germination. The diurnal fluctuations in temperature caused the higher germination rate. The germination rate of the seed stored in the water at 5°C for 2 to 4 weeks was accelerated in comparison with the outdoor dried storage. Though the germination rate improved from November to March by 5°C under water storage, the germination rate did not improve after April by this process. Seasonal variation in emergence was investigated. C. flaccidus emerged mainly in May outdoors under the flooding. Under drainage, the emerged rate improved from April to September. These seemed to relate with the amount of rainfall. Eleven herbicides were applied to C. flaccidus. Its sensitivity to sulphonylurea and pyrazol herbicides was low. From the observation in the field, C. flaccidus was found to grow in the gap of canopy. According to the results obtained here, the germination characteristic of C. flaccidus may be the adaptive ability into the gap of canopy. Moreover, sulphonylurea herbicide, which is widely used in Japan, has no effect on C. flaccidus. These may be the reason why does C. flaccidus infest the rice field in Japan.