ミズガヤツリの生活過程の解析と防除に関する研究

Abstract

The author investigated the physiological and ecological characteristics of C. serotinus, a perennial weed in paddy fields, during its whole life cycle, together with agronomic and chemical methods of control, and designed an effective integrated control system. This study was carried out at Chiba Agricultural Experiment Station during the period from 1966 to 1976.1. The life cycle is divided into 4 stages, emergence, propagation, tuber formation, and preparation for emergence. Reproduction occurs by seeds, tubers, base of shoots, base of new shoot-tubers, and stolon, but mainly by tubers.2. Characteristics and factors affecting tuber sprouting were analysed. The results indicated that oxygen supply is the most important factor for tuber sprouting, and that, in the fields, soil moisture content exerts an important influence on emergence from tubers in relation to oxygen supply.3. Effect of temperature, fertilizer elements and light on the propagation was examined. Results showed that competition for nutrients between rice plants and C. serotinus may be one of the reasons for the retarded propagation in rice fields, but the major limiting factor for the propagation of C. serotinus is presumed to be light intensity, since in any case the propagation was more inhibited when the growth of rice plant was more active compared to that of the weed.4. Factors affecting tuber formation were examined. Day-length as well as temperature was found to be an important factor affecting tuber formation, it appeared and that the number of tubers is determined by the number of plants, and also by the factors affecting propagation of plants.5. To analyse the effects of C. serotinus on growth and yield of rice, C. serotinus was planted at different times and different densities in paddy fields under various methods of rice cultivation. The results indicate that the dominancy of rice plants in the competition for light with C. serotinus causes less crop damage by the weed. The yield component which contributed most to the rice yield reduction was the decrease in panicle number, followed by the decrease in grain number per panicle.6. With regard to agronomic control methods, the effect of plowing and puddling was examined. Turn-over plowing in winter was effective to kill reproductive organs. Puddling was highly effective in killing both overwintering organs and shoots that have sprouted at the time of puddling, by burying them in the soil. Puddling combined with turn-over plowing in winter killed about 80% of the reproductive organs. In the fields of early season rice cultivation, plowing immediately after the rice harvest was also very effective in preventing tuber formation. In this case, rotary plowing was more effective than turn-over plowing.7. As for the herbicidal control, soil treatment after rice transplanting, foliage treatment with paraquat prior to puddling, and foliage treatment after rice harvest were analysed, and their suitability for effective control was evaluated.8. Based on the above results, an integrated control system for transplanted early-season rice cultivation was designed as shown in Fig. 9.