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.

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The present study was undertaken with a view to clarifying the properties of oxadiazon as a herbicide for transplanted rice and to developing effective application methods best suited to its properties.
Weed control effect of the herbicide on barnyardgrass was evaluated and the following results were obtained.
1) Oxadiazon application was most effective as a pre-emergence treatment. Weed control effect of the herbicide was reduced with the progression of the growth stages of barnyardgrass.
2) Oxadiazon was able to control barnyardgrass effectively in flooded water even at a concentration as low as 0.05ppm.
3) The deeper the incorporation of oxadiazon in soil, the lower was the herbicidal activity.
4) In the soil incorporation treatment, oxadiazon was effective in the control of barnyardgrass at the pre-emergence stage up to a depth of 2-3cm from the soil surface. However oxadiazon lost its effectiveness in the control of barnyardgrass when it was incorporated in deeper soil layers.
As for the phytotoxicity of oxadiazon to rice plants, the following characteristics were observed.
1) No toxic symptoms were recorded in rice plants at a concentration of oxadiazon below 0.2ppm in flooded water.
2) The deeper the incorporation in soil, the less was the phyototoxicity to transplanted rice plants.
3) The highest degree of phytotoxicity in rice plants was observed when the seedlings were transplanted with the entire root zone located in the oxadiazon treated layer.
4) A negligible degree of phytotoxicity was observed in rice seedlings with newly developed roots coming in to contact with the oxadiazon-treated layer.
5) The characteristic symptom of oxadiazon toxicity was the appearance of browning in newly developed leaves.
6) Leaf browning was the external manifestation of browning of the assimilatory tissues. No adverse effect of oxadiazon was observed in other tissues.
7) In general, the degree of leaf browning (browning in both leaf sheath and lamina) tended to be directly proportional to rice growth inhibition. A minimal degree of leaf sheath browning did not exert a deleterious effect on the growth of rice plants.
8) Oxadiazon absorbed by the roots was readily translocated to the shoots.
Based on the properties of oxadiazon as a herbicide for transplanted rice, to achieve effective weed control with minimum or no phytotoxicity to rice plants, oxadiazon should be applied in layers located at a 2-3cm depth from the soil surface. A flooded condition should be maintained after the treatment and the final concentration should not exceed 0.2ppm in the flooded water to avoid damage to rice plants.
To satisfy the above conditions at the time of application of oxadiazon an effective, economic and easy application method suited to different types of soil and acceptable to a large number of farmers was developed as follows: the hebicide in the form of an emulsifiable concentrate is scattered directly over the water surface before or immediately after final puddling of the field.

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1. Seeds of jointvetch are very hard and display dormancy when fully ripe. On account of their dormancy, the time required for the emergence of the plant is usually long and variable. In the experiments conducted in Kanagawa Prefecture, however, the weed emerged throughout the year except in the frost season.
2. Soil conditions characterized by a saturated moisture level were more favorable for the emergence of jointvetch seed than submerged soil conditions and the emergence ratio seemed to increase with shallow flooding during the period of drainage associated with rice transplantation.
3. Jointvetch was highly sensitive to pre or early post-emergence treatment of diphenyl ether, s-triazine and phenoxy types herbicides. However, f oliar application of herbicides could not control jointvetch perfectly when the plant height exceeded 20cm. For example, paraquat killed the leaves already developed but the new leaves developed after the treatment and the axillary buds grew normally.
4. Commercial herbicides which are able to control jointvetch are effective when applied during the period from the pre-emergenc to the first-leaf stage of this weed.
Moreover, the emergence of the weed takes place during a comparatively long period of time. Therefore, it is recommended to apply suitable herbicides successively twice to 3 times for instance, once before transplanting of rice or once or twice after transplanting.

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Inhibition of photosynthesis, plant growth and seminal root elongation was evaluated to investigate the difference in the effect of herbicide injury between naked barley and wheat. The results were as follows.
1. Foliar application of photosynthesis inhibitors such as ioxynil, prometryn, diuron and linuron resulted in a more pronounced decrease in the photosynthetic rate of naked barley compared with wheat. The effect of prometryn, diuron and linuron applications was particularly conspicuous.
2. Photosynthesis and plant growth were more severely inhibited in naked barley than in wheat following the combined application of diuron and dichlobenil, prometryn and dichlobenil, respectively.
3. Inhibition of elongation of seminal root by dichlobenil was more severe in naked barley than in wheat, However, the same degree of inhibition was recorded in both species after the application of chloropropham, bentiocarb and trifluralin.

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Dynamics of weed communities in experimental shifting cultivation plots during the two years following the felling of the forest were investigated. The experimental site is located in northeast Thailand and maize was used as a crop. Eupatorium odoratum was the most dominant species in the shifting cultivation plots during the two year period studied. Yearly burning, however, depressed its regrowth. On the contrary, Ageratum conyzoides conspicuously increased in the second year. When weed species were periodically removed, Crassocephalum rubens became the dominant species. In the first year, a great number of individuals of C. rubens developed in the improved plots where plowing, manuring and weeding were done. In the second year, E. odoratum remarkably increased while A. conyzoides dominated in the non-weeded plot under improved conditions. During the first year after the felling of the forest, few grass weeds appeared. The floristic composition of buried seeds in the soil changed with the duration and/or method of cultivation.

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The effect of variations in the light and temperature on the germination of Leptochloa chinensis Nees seeds stored under different conditions was investigated.
1. The dormancy of seeds stored under air-dried conditions was readily broken when seeds placed on a moist filter paper were subjected to a regime of 12 hours light at 40°C and 30°C and 12 hours dark at 40°C and 15°C, respectively.
2. Light played a major role in the breaking of dormancy. The effect of light on seeds stored under air-dried conditions was more conspicuous 6-12 hours after water absorption than at the onset.
3. The degree of breaking of dormancy varied with the conditions of storage, and it was higher in the following order, moist conditions at 5°C<air-dried conditions at 5°C<air-dried condidtions at room temperature<upland field conditions. However the breaking of dormancy under these conditions of storage did not result in seed germination when seeds were continuously exposed to darkness at 30°C.

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Experiments on the competition of weeds with grain sorghum (Sorghum bicolor (L.) Moench) in relation to changes in the weeding period were conducted to determine whether the interval between weedings which had been established in a previous report was appropriate.
1. Plant lenght of Digitaria ciliaris (Retz.) Koeler in the plot without weeding reached the upper part of crop canopies when relative light intensity was less than 10%, whereas in the plots where weeding intervals after seeding ranged from 20 to 40 days the plant length reached only the lower part of crop canopies.
2. The ratio of weed weight to total plant community weight was large in the plot without weeding while in the plots where weeding intervals ranged from 20 to 40 days, the ratio was below 4%.
3. At harvest a large amount of weeds remained in the plot without weeding while a small quantity of weeds remained in the plots where weeding intervals ranged from 20 to 40 days.
4. In the plot without weeding dry weight of plant and grain weight were reduced along with fodder dry weight. Crop yield reduction associated with weed growth did not occur in the plots where weeding intervals ranged from 20 to 40 days.
5. Based on these results and in taking into account the meteorological conditions during the year when the experiments were conducted, it appeared that a weeding interval of approximately 26 days after seeding was appropriate and enabled to avoid crop yield reduction associated with growth.

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