Alloxydim-sodium (ADS), sodium salt of methyl 3-(1-allyloxyaminobutylidene)-6, 6-dimethyl-2, 4-dioxocyclohexyl carboxylate, is a highly selective post-emergence graminicide. It was more than 100 times more active on corn than soybean in post-emergence treatment. The absorption, translocation and metabolism of ¹⁴C-ADS were studied to clarify the mechanism of the selectivity between corn and soybean. No great differences in the rate of the absorption by leaf were found between the two species at 1, 4, and 24 hours after treatment. Approximately 80% of the absorbed radioactivity was detected in the treated leaf 24 hours after treatment in both plants. In other parts, the highest ¹⁴C-concentration was in the stem for corn and in the first leaf for soybean. However, there was no great difference in radioactivity between the stem of corn and the second leaf of soybean, which have meristematic region respectively. The meristematic region was considered as a site of action of ADS in gramineous plant. A metabolism study was also conducted. TLC analysis of plant extracts from both corn stem and soybean leaf up to 168 hours after treatment with ¹⁴C-ADS revealed no evidence of ADS metabolism in corn and soybean. The selective action of ADS in corn and soybean cannot be accounted for by differences in its foliar absorption, translocation or metabolism in these species.

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Photosynthesis and transpiration activities of E. geniculata were examined under several conditions in comparison with E. hirta and corn plants. The results obtained are as follows:
1) E. geniculata, a C₃ plant, had a lower saturation light intensity for photosynthesis, ca. 50klux, while those of E. hirta and corn, both C₄ plants, were over 70klux and 75klux, respectively. The apparent photosynthetic rate under a strong light was limited by mesophyll resistance, r_m, in E. geniculata, but by stomatal resistance, r_s, in E. hirta and corn. The highest transpiration rate of E. geniculata was about two times that of E. hirta and corn. Stomatal closing reaction due to darkening was slower in E. geniculata than in the other two species.
2) A young leaf of E. geniculata had a higher saturation light intensity, maximum transpiration rate and maximum apparent photosynthetic rate than an old leaf did.
3) When grown under shading treatment, saturation light intensity for apparent photosynthesis was lower in E. geniculata than in corn. The degree of decrease in apparent photosynthesis under a strong light condition was larger in E. geniculata than in corn. The decreased apparent photosynthesis was attributable to increased r_m in E. geniculata, but to both increased r_m and r_s in corn. Shading treatment decreased transpiration rate in corn but not in E. geniculata.
4) The short-term water requirement of E. geniculata was more than twice that of corn under normal light, and further increased to approximately three times that of corn by shading treatment.
5) Maximum apparent photosynthesis in E. geniculata became smaller when day-length was increased. The highest maximum transpiration rate was obtained from 12-hour day-length, giving the lowest water use efficiency. Stomatal closing reaction due to darkening was far quicker in 8-hour than in longer hour plots.

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Herbicidal effects of soil treatment with fine granules of five herbicides and their residues in cabbage and ordinary crop field crops were investigated.
1. Nitralin, alachlor, pendimethalin and trifluralin applied to fields with consecutive cabbage croppings controlled more effectively the emergence and development of weeds in both the summer and winter croppings (Table 2).
2. Alachlor-linuron granules applied to fields cultivates with ordinary crops such as corn, sweet potato and peanuts in summer and trifluralin applied to cabbage fields in winter controlled effectively weeds (Table 3).
3. Although each herbicide applied to the summer cropping was not detected in soil after 140 days, concentration high enough to inhibit weed emergence was determined in soil even after 200 days in the winter cropping (Table 4, 5). In the summer cropping, the pattern of persistence of herbicides in soil differed from that in winter (Fig. 2).

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The effect of the water temperature on the leaf-emergence at the initial stage of the development in Echinochloa oryzicola VASING., Alisma canaliculatum A. BR. et BOUCHE and Scirpus juncoides ROXB. subsp. juncoides ROXB. under diurnal changes of water temperature was analyzed by measuring the effective cumulative water temperature. A method for the estimation of the progress of leaf-emergence in each type of weed depending on the region was developed based on the results obtained.
1. The coefficient of variation of the effective cumulative water temperature (Σθ_w) in each plot after sowing and before the leaf-emergence date depending on the diurnal variations of the water temperature was very small in comparison with the coefficients of variation of the number of days required for emergence, and of the cumulative water temperature for the daily minimum, daily maximum and the average temperature (Table 5).
2. Based on these findings, it was considered that Σθ_w could be used as an index with high accuracy the progress of leaf-emergence in each type of weed under various conditions of water temperature including diurnal variations. Using Σθ_w, the relationship between the diurnal variations of the water temperature and the progress of leaf-emergence of the weeds was quantified based on the type of weed and the depth of buried seeds (Fig. 5).
3. The variations in the date of emergence of the second leaf in each type of weed, associates with the changes of the date of the final puddling in a normal year in Sapporo, were analyzed. At the same time the data of emergence of the second and third leaves in each type of weed at 9 locations in Hokkaido was defined in relation to the changes of the air temperature of in a normal year. The number of days after the final puddling required for the emergence of the second leaf was the lowest (14 days) in Asahikawa for seeds of Echinochloa oryzicola buried at a depth of 0.2cm followed by Hakodate, Obihiro, Sapporo, Esashi, Rumoi, Muroran and Urakawa. The highest value (20 days) was recorded in Abashiri. When the daily mean temperature was 2°C higher than in a normal year, the number of days advanced by 2 to 3 days. When the temperature was lower there was a delay of 3 to 4 days. In Abashiri in particular there was an increase in the differences in the numder of days required for the emergence of the second leaf depending on the depth of buried seeds. At the same time, leaf-emergence become irregular (Fig. 5).
4. The method for determining the effective cumulative water temperature is as follows.
(1) The relationship between each constant for the water temperature (T) and the number of days required for an increase of 0.2 leaves at the initial stage of growth of the weed (D) is represented by the equation: D=T/-a+bT (a and b are constants depending on the type of weed) (Fig. 1).
(2) In the above-described equation T_a is estimated for the lowest value of T_i×D_i, and α_i satisfying the equation: α₁·T₁·D₁=α₂·T₂·D₂=…=α_n·T_n·D_n is derived by the equation: α_i=T_a·D_a/T_i·D_i, and then α_i·T_i is expected as θ_wi (effective water temperature) (Table 2).
(3) Product summation of θ_w obtained for each value of water temperature with an increment of 2°C and the time when the increment of the water temperature is observed

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Effect of simetryn [2, 4-bis (ethylamino)-6-methylthio-s-triazine] and dimethametryn [2-(1, 2-dimethylpropylamino)-4-ethylamino-6-methylthio-s-triazine] on growth and photosynthesis of rice (Oryza sativa L.) cultivars Nihonbare and Choseng Tongil, and barnyardgrass (Echinochloa oryzicola Vasing.) was compared. Dimethametryn showed greater phytotoxicity than simetryn in all plants, but difference in susceptibility of the plants to the herbicides was greater in Nihonbare cultivar than in other plants. It is believed that this results from very high tolerance of the cultivar to simetryn.
Both herbicides inhibited in photosynthesis with very low concentrations, and dimethametryn was the stronger inhibitor. The I₅₀ values in the reaction were approximately 4 or 5×10^-8M and 2×10^-8M for simetryn and dimethametryn respectively.
This difference in inhibiting activity at the site of action is considered to be one of the factors determining their phytotoxicity.

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In order to clarify the mechanism of differential phytotoxic activity of herbicides simetryn (2, 4-bis(ethylamino)-6-methylthio-s-triazine) and dimethametryn [2-(1, 2-dimethyl-propylamino)-4-ethylamino-6-methylthio-s-triazine], their absorption, translocation and metabolism were investigated in rice (Oryza sativa L.) cultivars Nihonbare and Choseng Tongil and barnyardgrass (Echinochloa oryzicola Vasing.). The plants were grown in water culture to the 3-leaf stage and their roots were treated with 10^-5M of ¹⁴C-simetryn and dimethametryn. Rice cultivars absorbed both herbicides at similar rates, while barnyardgrass absorbed dimethametryn more quickly. Simetryn moved to shoots faster than dimethametryn in all plants. In Nihonbare, ¹⁴C concentration in shoots was significantly higher after simetryn treatment, while no difference was observed in Choseng Tongil and barnyardgrass. Nihonbare metabolized simetryn more quickly than dimethametryn. This may indicate that difference in metabolic activity determines tolerance to the herbicides. In Choseng Tongil and barnyardgrass, the rate of simetryn metabolism was much slower than Nihonbare, and no clear difference was observed in metabolic activity between the two herbicides. This may explain the similar phytotoxic effect of the herbicides on Choseng Tongil and Barnyardgrass. The results indicate that the slower metabolic rate of dimethametryn is one of factors in its greater phytotoxicity.

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In order to establish efficient methods of control of the arrowhead weed (Sagittaria trifolia L.) in paddy fields in Japan, the longevity of the weed tubers in paddy fields was examined from 1981 to 1983, as the longevity of the tubers in paddy soil had not been studied. Seasonal changes of the tubers which survived in the paddy fields were studied from 1982 to 1983. Effect of drying or cutting on the longevity of the tubers was also analysed in relation to the effect of rotary tillage.
The results obtained were as follow;
(1) The tubers were distributed in the soil from the surface layer to the layer under the plow sole. The tubers in the surface layer were smaller in size, and those in the layer under the plow sole were larger.
(2) The larger tubers tended exhibit a deeper dormancy than the smaller ones as determined by incubation with immersion in water at 25 or 30°C and under on illumination of at 5, 000lx (24 hours). However, after rice transplanting, the dormancy of the majority of the tubers was broken.
(3) About more than half of the tubers in the soil were injured by rotary tillage in the spring, and among the tubers which divided, only those in which the growing points of the terminal buds were included were able to sprout. The tubers were not injured by puddling.
(4) The living tubers gradually disappeared from the soil subjected to repeated rotary tillage in the spring and by emergence of the weed during the rice growing season. The number of tubers rapidly decreased after midseason drainage, and few tubers were observed at harvest in the autumn following the formation of tubers.
(5) The tubers died due to drying after being placed on the soil surface for six days and after about eight weeks when placed in non-irrigated soil at a depth of five centimeters under glasshouse conditions. This suggested that only a few tubers would therefore be killed in the field even if they were distributed at the surface of the soil through tillage.
(6) The results obtained suggest that the propagation of the tubers of the arrowhead weed in the following year is negligible since tuber formation would not be able to occur in the season, because the longevity of the tubers is less than one year.

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