Morphological effects of bensulfuronmethyl application to rice plant and their safening effect by its dimepiperate mixture application were investigated under various paddy soils and dosages of herbicides.
1) Experiments were carried out by using three kinds of soil; clay loam (paddy soil of Chugoku National Agricultural Experiment Station), mixture of sand and clay loam (1:1) and sandy loam (paddy soil of Kagawa Prefectural Agricutural Experiment Station). The growth inhibition of rice in shoots by bensulfurnomethyl application was severer by planting on the mixture of sand and clay loam and sandy loam which had lower CEC and clay content, than by planting on clay loam, and the recovery from growth inhibition on sandy loam tended to be later than on clay loam and the mixture of sand and clay loam. Effects of bensulfuronmethyl application on roots of rice were observed as the inhibition of root elongation and the decrease of root number at shoot units which emerged just after the herbicide application, and the degree of the influence appeared the severer in the order of the mixture of sand and clay loam>sandy loam>clay loam.
2) Herbicides were applied to rice plants grown on the clay loam plots at two dosages, 300 and 600g/a as commercial products. Severe growth inhibition of shoots and roots was observed in the case of applications at 600g/a. At severely affected shoot units, the root elongation was markedly inhibited, and the number of crown roots also decreased.
3) Safening effect in rice of the combined application of bensulfuronmethyl and dimepiperate was confirmed in experiments involving three kinds of paddy soils and two dosages of herbicides.
4) Injury to rice was found to appear in organs of successive shoot units, growing simultaneously.

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The analysis of the environmental factors which are related to the duration of the period from emergence to heading or flower-bud formation is an important approach to understand the reproductive strategy of weeds.
Therefore, a simple model that can predict the dates of heading or flower-bud formation in D. adscendens, E. crus-galli and C. album was developed by computing the daily daylength and mean air temperature after emergence.
That is, DVS(n)=ΣDVR(i)…(1) DVR(i)=aL(i)+bT(i)+c…(2)
where DVS (n) is the developmental stage at n-th day after emergence; DVS is zero at the onset of emergence, 1.0 at heading or flower-bud formation; DVR (i) is the developmental rate at i-th day after emergence; L (i) and T (i) are the daylength (hr) and mean air temperature (°C) of i-th day, respectively; a, b and c are parameters. The value of the parameters was determined by multiple regression analysis based on data of field experiments. The results obtained were a=-0.0076, b=0.0018 and c=0.091 for D. adscendens, a=-0.0071, b=0.0014 and c=0.093 for E. crus-galli and a=-0.0137, b=0.0023 and c=0.156 for C. album.
The prediction by the above-mentioned model showed a good fit to the values observed based on field experiments carried out for three consecutive years and the phytotron experiments (daylength=12hr, temperature=25°C).
The relation between the duration of the period from emergence to heading or flower-bud formation and seed production characteristics of weeds was discussed.

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To analize the processes controlling the breaking of dormancy of tubers in an arrowhead (Sagittaria trifolia L.) under natural conditions in paddy fields, studies on the breaking of dormancy of a tuber population and the sprouting response of a population of non-dormant tubers were carried out. All the experiments were performed in incubators at a controlled temperature.
The results obtained are as follows;
1) To analyze the process of acquisition of dormancy during the formation of the tubers, the sprouting ability was tested from the period of elongation of the storage rhizomes (mid-September) until the final stage of tuber formation (late-November). The population of tubers entered a deep dormancy at the zone of separation from the mother plant.
2) The sprouting process was investigated under light (5, 000lx.) conditions in moist upland soil at a temperature of 30°C by subjecting the plants to various storage conditions including changes of the ambient temperature, soil moisture conditions, storage period to analyze the process of breaking of the primary dormancy. The pattern of tuber sprouting was varied with the temperature, the soil moisture conditions during the storage, and the storage period.
3) The tuber dormancy was broken with a low ratio of mortality and absence of sprouting during the storage period, when the tubers were stored in moist upland soil for more than 3 weeks at a temperature of 30°C. At constant temperatures varying from 5°C to 15°C, sprouting took place later than at 30°C.
When the tubers were stored at room temperature, sprouting occured earlier than when they were stored outdoors.
4) When the tubers were stored in submerged soil, they died rapidly at the temperature of 30°C. On the other hand, sprouting occurred earlier at the other temperatures and the longer the storage period, the earlier the sprouting.
5) Secondary dormancy of the tubers could not be induced.
6) Time courses of the sprouting of non-dormant tubers at temperatures in the range of 10-40°C were analized. Constant temperatures of 25, 30°C or an alternating regime of 30/15°C were the optimum temperatures for sprouting. Minimum and maximum temperatures for sprouting were about 10°C and 35-40°C, respectively.

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This study was carried out to identify thiolcarbamate compounds with superior intergeneric selectivity between rice and barnyardgrass (Echinochloa oryzicola), that could be safely applied during the germination and seedling stages of rice.
1) In the substitution of the thiolcarbamate compounds, it was essential for the enhancement of the selectivity between rice and barnyardgrass that the amine part be a cyclic amine and ester part belong to the cumyl group (α, α-dimethyl-benzyl group) (Tables 2-6).
2) Dimepiperate (S-1-methyl-1-phenylethylpiperidine-1-carbothioate) was selected out of 65 substituted thiolcarbamate compounds due to it's high herbicidal activity against barnyardgrass, it's structure consists of a cyclic amine with 5 methylene rings, as in the case of piperidine. Dimepiperate exhibited a higher selectivity toward seeded rice than thiobencarb and molinate (Figs. 1-2).
3) In the pot tests carried out in the greenhouse under submerged conditions, dimepiperate showed a higher herbicidal activity in the pre than post emergence treatment of Echinochloa oryzicola (Eo), Monochoria vaginalis (Mv) and Scirpus juncoides (Sj). The herbicidal activity of this compound which was particulary high against Eo was comparable to that of thiobencarb and molinate, but was lower against Mv and Sj than that of the conventional herbicides.

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Safening action of dimepiperate in rice plant (S-1-methyl-1-phenylethylpiperidine-1-carbo thioate) was examined.
1) Dimepiperate showed an obvious safening action on herbicides inhibiting root growth, such as pendimethalin, clomeprop, MCPB, bensulide and bensulfuron methyl (Table 3). The action was markedly different from that of usual safeners.
2) Safening action of dimepiperate in rice plant was more remarkable than that of other herbicides (dimepiperate>thiobencarb>>mefenacet) (Fig. 2). Dimepiperate alleviated the root injury caused by bensulfuron methyl, and the optimum dose for the ratio of bensulfuron methyl/dimepiperate was 1:3-1, 000 (Tables 4, 5, Fig. 1).
3) Safening effect of dimepiperate on the auxin-type herbicides MCPB, Phenothiol and clomeprop was manifested by the alleviation of the root injury caused by these compounds. It is suggested that the addition of dimepiperate enable to extend the application period, while MCPB and phenothiol cannot be applied to the rice plant beyond the 5-leaf stage (Fig. 3). The safening effect of dimepiperate may contribute significantly to the alleviation of the phytotoxicity caused by auxin herbicides which is observed at high temperatures (Fig. 4). Though the mixture rate of dimepiperate and auxin herbicide required to achieve both a herbicidal and safening effect, has not been fully investigated the range of 1:1-30 for the auxin herbicide and dimepiperate (Tables 6, 7) is proposed.

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Broom (Cytisus scoparius LINK) prevents vegetational succession in Etajima and Takehara in Hiroshima prefecture, where it was planted to re-establish natural forests. The allelopathic effects of broom were studied by bioassays using lettuce seeds.
The results are as follows:
1. Stems and leaves of broom contained relatively strong allelochemicals (Table 1), which leached out by rain drops (Table 2).
2. Allelochemicals from broom accumulated in ‘Masa’ soil (immature yellow soil derived from granite) containing a small amount of organic matter and inhibited seed emergence (Table 3). However in the soil containing a large amount of organic matter, the inhibition of root growth of lettuce was not appreciable (Fig. 3).
3. Sparteine, which is a bioactive substance contained in broom, was not the major allelochemical substance (Fig. 4). Hydrophilic substances with positive charges from broom exhibited a strong allelopathic activity (Table 4, 5).
4. Allelochemicals which leached out from the stems and leaves of broom plants by rain accumulated in soils and inhibited the root growth of the seedlings of other plants.

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Resistance to paraquat of the leaves of Erigeron philadelphicus which were collected from 64 sites in 30 cities, towns and villages in Ibaraki Prefecture was surveyed after soaking leaf disks in 4×10^-5M paraquat solution for 20-24 hours at 25°C at a light intensity of about 10klx.
Paraquat-resistant biotypes were detected in 13 sites out of 64 and showed a comparatively uniform distribution in the areas surveyed (Fig. 2). Paraquat-resistant biotypes were found in orchards, mulberry and tea fields, parks, shrine gardens and gardens of houses, but were not found in the periphery of orchards, mulberry and tea fields, and in upland fields and periphery, periphery of paddy fields, roadsides, bamboo groves and estate groves (Table 2). These facts indicate that the existence of resistant biotypes is closely related to the type of land use.

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