(1) Modes of the selective action of several herbicides on plant species, especially gramineous plants, were studied from the biochemical and physiological viewpoints. Not only for agricultural practice but also for scientific interest is the selective action of hercicides one of the most important aspects of their function because various characteristic to plant species can thus be revealed. In the study, the mechanisms underlying the selectivity of herbicides were traced through investigations of their absorption by either roots or shoots of plants, translocation in plant tissues or organs, chemical transformation by plant metabolism and effects on plant metabolic systems. Contribution of each process to the selectivity was evaluated by comparing these processes among plant species. How each process limits the concentration of the active chemicals in plants as well as their affinity to action site (s) was also considered. Use of herbicides labeled with radioactive isotopes was found to extremely informative for this type of study.
(2) Selectivity of propanil between rice and barnyardgrass was studied at first. By using carbonyl-¹⁴C-labeled propanil with organic phosphorus insecticides such as dipterex it was shown that the absorption was not a rate-limiting process in the selectivity. It was also shown that rice leaves hydrolysed considerably the compound to 3, 4-dichloroaniline and acid unlike barnyardgrass. Out of series on N-(3, 4-dichlorophenyl)-alkylcarboxamides and N-(chloro-substituted-phenyl)-ethylcarboxamides, only a few were found to be hydrolysed by barnyardgrass. It was concluded that barnyardgrass had arylacylamidase activity with a substrate specificity strictly limited in anilides. Solan, cypromid or CMPT were not hydrolysed by rice plants.
Thiadiazolylurea derivatives such as DBTU were synthesized as potent herbicides and N-demethylation was found to be the mechanism of detoxification. Cotton seedlings whidh are very tolerant to diuron were susceptible to DBTU and lacked the N-demethylation detoxification mechanism of the latter. Substrate specificity of the demethylating enzyme from different plant species was investigated.
(3) When propanil was applied at very low concentrations to roots of rice and barnyardgrass for several days, selectivity between the two species was achieved. Photosynthetic activity of barnyardgrass leaves decreased, unlike that of rice leaves. Concentration of propanil in leaves and recovery rates from the inhibition were investigated and a mechanism other than the hydrolytic degradation was proposed to account for the tolerance of rice to propanil.
(4) Several examples of herbicide selectivity where either absorption or translocation was the main limiting factor were identified. Orbencarb was shown to be absorbed more by crabgrass than by wheat, suggesting that the former plant may be susceptible to the herbicide due to its enhanced absorption. Barban showed a selectivity between wheat and oat. When it was applied to intact oat leaves, protein and RNA synthesis was markedly inhibited unlike in wheat. However when it was applied to leaves that had been cut in section protein and RNA synthesis in both plant species was similarly inhibited. It was observed that thiochlormethyl was actively translocated from the roots to the shoots in susceptible plants such as tomato compared with tolerant plants such as rice or cucumber.
(5) In an attempt to gain a better understanding of the specificity to herbicides of a large number of plant species, comparison between cultivated varieties was made. It was found that some of the japonica type varieties of rice were much more tolerant to simetryn than some of the indica and japonica×indica hybrid-types. The former metabolized almost 90% of the simetryn applied within 24 hours while the latter only less than 50%.
(6) Effect of ambient temperature on the selectivity of simetryn was studied.

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K-503 exhibits a higher herbicidal activity in the pre-emergence treatment than in the post-emergence treatment. Plants treated first display chlorosis along the veins of the leaf, followed by complete chlorosis and death of the leaf.
The study was carried out to analyse the selectivity and inhibitory effect of K-503 on pigment biosynthesis.
(1) In the greenhouse pot test, Digitaria adscendens, Setaria viridis, Portulaca oleracea, Amaranthus viridis, Polygonum lapathifolium, Cyperus microiria were completely controlled by a pre-emergence treatment of K-503 at the rate of 2.5g/a with no adverse effect on cotton and sunflower (Table 4).
(2) The order of crop tolerance to K-503 in pre-planted soil incorporation treatment was as follows; cotton, sunflower>>soybean, radish>tomato, sugar beet>>rice>corn, wheat>cucumber (Table 5).
(3) In the outdoor pot test, no phytotoxic effect on cotton and sunflower, irrespective of varieties, was detected in the pre-emergence treatment of K-503 at a rate of 60g/a (Table 6).
(4) From the results of the field test, K-503 was considered to be a very promising new pre-emergence herbicide in cotton and sunflower fields (Table 7).
(5) It was shown that K-503 inhibited the dehydrogenation reaction of phytofluene to ζ-carotene in the carotene biosynthesis, and caused the photodecomposition of chlorophyll under strong illumination (Fig. 1-4).

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During the period from July to August 1981, studies were carried out to evaluate the relationship between some environmental conditions and the distribution of aquatic weeds growing in the irrigation canals of the paddy area located in the basin of the Ibi River over a distance of 56km from the estuary to the upper reaches of the river, in the western part of the Nobi Plain.
The area surveyed was divided into 51 units each covering a surface of 16km². The area was further subdivided into three groups including the upper reaches, the central part and the lower reaches of the river. Within each unit various species of aquatic weeds excluding Phragmites communis Trinius and Zizania latifolia Turcz. were sampled to analyse the frequency of their appearance in the basin of the river. On the basis of these studies, 5 groups of aquatic weeds were identified as follows: Group A: Weeds occurring throughout the basin of the river (11 species): Spirodela polyrhiza (L.) Schled., Lemna paucicostata Hegelm., Hydrilla verticillata (L. f.) Casp., Elodea nutalli (Planch.) St. John, etc. Group B: Weeds distributed from the lower reaches to the central part of the river (7 species): Hydrocharis dubia (Bl.) Backer, Ceratophyllum demersum L., etc. Group C: Weeds distributed in the lower reaches of the river only (15 species): Paspalum distichum L., Potamogeton pectinatus L., Ruppia maritima L., etc. Group D: Weeds distributed from the central part to the upper reaches of the river (2 species): Sparganium erectum L. and Potamogeton malaianus Miquel. Group E: Weeds distributed in the upper reaches of the river only (1 species): Batrachum nipponicum (M.) Kitam. var. major (H.) Kitam.
Studies on the environmental conditions of the waterways including the presence of current as well as the properties of the water such as pH, content in Cl^-, Ca, K, Na and Mg revealed significant differences among the three zones of the river basin. Based on the results obtained, it is suggested that the difference in the frequency of distribution of the aquatic weeds within the various zones of the river basin is related to environmental factors which control the growth of the weeds.

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The existence of intraspecific variations for certain characters in Cyperus serotinus Rottb. in Kanagawa Prefecture was described in a previous report. Variability in tuber dormancy, tuber germination and viability of young shoots among 22 strains was evaluated in this study.
(1) High percentage of germination was obtained in the top tuber of all strains in January and March. In the middle tuber, however, a high percentage of germination was obtain ed in all the strains in March, while a few strains (No. 4, 5, 11) showed a low percentage in January. These findings suggest that variation among the strains in the degree of tuber dormancy was not observed in the top tuber, while in a few strains the middle tuber may have remained dormant in January.
(2) In the study of tuber germination of 22 strains under 2 conditions (in water, in boiled water), statistical analysis showed significant differences at 1 percent level in the germination percentage, onset of germination, mean value of germination days, number of shoots per tuber, young plant height, fresh weight of shoots, fresh weight of roots, fresh weight of shoots/fresh weight of tuber and increase in the rate of plant height per day among the strains. Also these differences were more significant under strong reduction conditions (in boild water).
(3) Of all the correlations between fresh weight of tuber and germination percentage, fresh weight of young shoots or increase in the rate of plant height per day, a low correlation coefficient was obtained except for the fresh weight of young shoots under mild reduction conditions (in water). Especially the correlation coefficient between fresh weight of tuber and the above mentioned characters showed negative values under strong reduction conditions (in boiled water). These findings suggest that the differences in these characters among the strains are due to quantitative differences of the tuber (tuber weight) as well as qualitative ones.
(4) The differences in germination viability of tuber and early growth among the strains would suggest the importance of investigations on these characters in relation to weed control in order to improve the control measures at the early stage.

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Tuberization of Cyperus serotinus Rottb., a perennial weed in paddy rice, is known to be enhanced under short day condition and to vary with time among the regions of Japan.
Twenty-two strains of Cyperus serotinus Rottb. collected from 18 locations in Kanagawa prefecture were grown under natural day length and the time of tuber formation was examined.
Results are as follows.
(1) These strains were found to show differences in the time of tuber formation; the earliest formation was on September 5 in Strain No. 18 and the latest on September 25 in Strains No. 4, the range of variations between the strains being 20 days.
(2) Tuber formation was more delayed than heading in all the strains used at intervals of 6 days (No. 11) to 38 days (No. 4).
(3) A low correlation coefficient (r-0.025) was obtained between the heading time and the time of tuber formation. Therefore, it may be concluded that the two responses of the strains used, namely heading and tuberization were independent from one another.

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Herbicidal activity and behavior of UY-510, N-[(R)-2, 3-epoxypropyl]-N-[(R)-α-methylbenzyl]-2, 4, 6-trimethylbenzenesulfonamide, were examined. The substance strongly inhibited shoot elongation, especially in barnyardgrass, without any effect on the germination of rice, barnyardgrass or radish even at 3, 000ppm in a petri dish test (Table 1).
UY-510 exhibited a higher herbicidal effect in the pre-emergence treatment than in the post-emergence treatment in a pot test (Table 2). Rice plants showed good tolerance to UY-510 and no phytotoxicity was observed when it was applied at their 2 leaf stage (Tables 3, 4, 5). In addition, the herbicide had lower mobility in soil than other herbicides (Fig. 1) and a good residual effect.
Thus, UY-510 was found to be quite a promising new herbicide for barnyardgrass control in fields where direct-sowing cultivation of rice is practiced.

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