The weedy form of Yellow nutsedge (Cyperus esculentus L.) has recently invaded arable land in Japan. In Kyushu, it was first detected in the paddy fields of early-season culture of rice in the Amakusa district, Kumamoto Pref. in 1990. Emergence, growth and tuber formation of C. esculentus were investigated in paddy fields in southern Japan.
1) In severely infested paddy fields in Hondo City and Reihoku Town in the Amakusa district, 9, 600-10, 000 new tubers and 1, 900-2, 400 aged tubers per m² were observed in soil at a depth of 8cm. The mean fresh weight per single new tuber was 82mg and 60mg for the samples from Hondo and Reihoku, respectively (Table 2).
2) Three experimental cropping practices of rice plants were compared to analyze the growth and tuber formation of C. esculentus (Table 1). The emergence and growth of C. esculentus in the A-season culture, plowed on April 20, were more conspicuous than in the C-season culture, plowed on June 19, while in the B-season culture, plowed on May 13, the emergence and growth were the least conspicuous. It was considered that the B-season culture corresponded to the most susceptible stage of C. esculentus to the damage by plowing and puddling, due to the depletion in nutrients in the mother tubers and immaturity of the new tubers. Midseason drainage for one week increased the number of new shoots which sprouted regardless of the season of cultures (Table 3). The number of tubers formed during the rice cultivation period was the largest in the A-season culture with midseason drainage (Table 4). A highly significant correlation was recognized between the number of tubers and top dry weight of C. esculentus at harvest time depending on the season of culture and water management (Fig. 2).
3) Tubers placed on moistened filter papers at 30°C sprouted three days after placement, and final sprouting occurred in 94% for the new tubers and 24% for the aged tubers (Table 5). When the soil moisture ratio was 50% at 30 and 18°C, more than 90% of the tubers emerged from the soil at a 3cm of depth until three and eleven days, respectively (Table 6). Tubers subjected to a soil moisture ratio exceeding 100% were unable to emerge at 30 and 18°C until twenty days after burying. However, they started to emerge under both temperature conditions two to three days and five to eight days after the soil moisture ratio decreased to around 80% (Fig. 3)

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Glutamine synthetase (GS) in shoots of cucumber, rice (C₃ plants), corn and barnyardgrass seedlings (C₄ plants), inhibited by glufosinate (2-amino-4[(hydroxy)(methyl)phosphinoyl]butyric acid), was separated by DEAE-Sephacel column into two fractions (GS₁ and GS₂). In cucumber and rice seedlings, the GS₁ activity was found lower than the GS₂, while the GS₁ activity was higher than the GS₂ in corn seedlings, and the two were almost equal in barnyardgrass seedlings. These results showed that cucumber and rice generally have a great deal of ammonia released from photorespiration and that GS₂ is implicated in assimilation of the ammonia. Corn and barnyardgrass, on the contrary, have little ammonia released from that cycle so that GS₂ activity was much less than GS₁. In root, only a single peak of GS activity was detected and was called GS_r.
Optimum pH was between 6.0 and 7.0 and optimum temperature was between 40 and 45°C for GS activities of the 4 seedlings. The KCl concentrations eluting GS₁ from column were similar to those of GS_r, and those of GS₂ were higher than GS₁ in all the plant species.
GS₁, GS₂ and GS_r activities were decreased by increasing concentrations of glufosinate, and the concentrations necessary for inhibition of the activity by 50% (I₅₀) were determined. In all four plant seedlings, I₅₀ values of glufosinate for GS₁ and GS_r were not greatly different, I₅₀ of GS₂ was obtained on the order of 10^-6M, while I₅₀ for both GS₁ and GS_r was on the order of 10^-5M. The roles of the GS isozymes in ammonia assimilation and their inhibition by glufosinate in C₃ and C₄ plants were discussed.

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Effects of plowing and herbicide application on the vegetation dynamics were examined in two types of uncultivated upland fields, one without tillage for 5 years and the other where plowing was carried out once a year. The restoration processes of the vegetation in the fields were analyzed during a period of 3 years in terms of floristic composition and degree of succession. In the fields without tillage for 8 years, the degree of succession increased to a value of more than 1000, the flora being dominated by Pueraria lobata and Solidago altissima. In the fields where plowing was carried out 4 times annually, the degree of succession decreased, the flora being dominated by grasses such as Digitaria ciliaris and Setaria viridis. When herbicides (paraquat) were applied twice a year, the degree of succession decreased in the fields without tillage prior to the herbicide application and increased in the fields where plowing was carried out once a year, with Pueraria lobata dominating in both fields. It was concluded that plowing 4 times a year is suitable for the restoration of degraded fields unlike the sole application of herbicides.

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The product of the number of hills per m² and shoot length of the weed plant, which is related to the formation of tubers, was selected as an index of tolerable growth level for the control of weed propagation in rice fields. The relationship between the reduction of rice yield and the weed quantity was studied in field experiments in which herbicides were applied for a period of three years to the water chestnut, Eleocharis kuroguwai Ohwi. The results obtained are as follows;
1. The proportion of the yield components contributing to the reduction of rice yield by the water chestnut was as follows. For the ear number, 1000-kernel-weight, percentage of ripened grains and number of grains per head, the proportion was 40.5, 27.8% and 16% each, respectively.
2. The correlations between the weight of winnowed paddy rice and the product of the number of hills per m² and shoot length of the weed plant were statistically significant during the experimental period (Table 2). The product of the number of hills per m² and shoot length of the weed plant was an effective index for the diagnosis of the amount of weeds in relation to the control of propagation.
3. The upper limit of the number of sprouting tubers in spring, which did not affect the rice yield, was 1.0/m², that of the number of hills in the midseason drainage was 7.2/m², and the upper limit of the product of the number of hills and shoot length of the weed plant at the stage of tuber formation was 11.7/m² (Table 3).
4. The upper limit of the number of sprouting tubers in spring, which reduced the rice yield to 95% of the yield in the weed-free plot, was 4.4/m² that of the number of hills in the midseason drainage was 15.6/m², the upper limit of the product of the number of hills and shoot length of the weed plant at the stage of tuber formation was 30.0/m² (Table 3).

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Activities of acetolactate synthase (ALS) of 10^-8 M bensulfuron methyl (BSM)-resistant carrot cells were compared with those of susceptible (normal) cells.
ALS activity, assayed by measuring acetoin formed by decarboxylation of acetolactate, was inhibited in normal cells by low concentrations of BSM. However, nearly or more than half of the total activity was not inhibited by 10^-6M BSM at pH lower than 7.5. Acetoin amounts produced in undecarboxylated samples almost coincided with those inhibited by high concentrations of BSM, 10^-6 and 10^-4M, in normal and resistant cells, respectively. This might indicate the presence of a direct acetoin producing system in ALS assay. Net ALS activity could be obtained by subtracting the undecarboxylated value from the total activity.
Optimum pHs were broad, around 8.5 for ALS and 7.0 for direct acetoin producing activity. ALS was saturated at 40mM pyruvate and apparent Km value for ALS was 5-6mM.
ALS from resistant cells was inhibited by BSM less than the normal cells. The BSM concentrations inhibiting ALS activity by 50% (I₅₀) were 1×10^-8M and 6×10^-7M for normal and resistant cells, respectively. As this I₅₀ value of the resistant cells was about 10 times higher than that reported previously (5.2×10^-8M), the probability is that insensitivity of ALS to BSM of the resistant cells developed during long-term culture.

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In the current studies, two experiments were carried out in a glasshouse to analyse the effects of competition from L. perenne seedlings on the growth of R. obtusifolius seedlings. In the first experiment, the contribution ratio of the effect of competition from shoot and root of L. perenne on R. obtusifolius seedling growth was investigated using Wagner pots (1×5, 000^-1a) which were divided into two parts. In each half of a pot 60 seeds of L. perenne (cv. Friend) or three R. obtusifolius seeds were planted and competition above-ground was controlled by using an acrylic resin transparent panel (35cm×25cm) while competition below-ground by using a polyvinyl chloride panel (Fig. 1). In the second experiment, the effects of seeding rate of L. perenne with or without cutting on R. obtusifolius growth were studied in a container box (volume; 361, 30cm×40cm×30cm) in which four seeds of R. obtusifolius were sown in a systematic pattern with L. perenne at the rates 2, 000g seeds/a (high) and 300g seeds/a (low). The results are summarized as follows:
(1) Competition from shoot and root of L. perenne significantly affected the shoot and root growth as well as the morphological characteristics of the seedlings of R. obtusifolius. The growth of the seedlings of R. obtusifolius was depressed heavily under the conditions of full competition including shoot and root competition followed by shoot competition only, root competition only and no competition from L. perenne (Table 1).
(2) Shoot competition for light exerted significantly higher influence on the growth of R. obtusifolius seedlings than root competition for soil moisture and nutrients (Table 2).
(3) Growth of R. obtusifolius seedlings was depressed mostly at a high seeding rate of L. perenne without cutting of L. perenne followed by low seeding rate without cutting, high seeding rate with cutting and low seeding rate with cutting. R. obtusifolius seedling growth was limited by the large number of. L. perenne seedlings, especially without no cutting which resulted in competition for light, soil moisture and nutrients (Table 3).
(4) These results suggest that for eradicating R. obtusifolius seedlings for the restoration of a pasture, it is necessary to enhance competition, especially shoot competition from L. perenne. Therefore the high seeding rate of L. perenne enabled to obtain dense forage stands quickly after seeding which resulted in the reduction of the light available for the growth of R. obtusifolius seedlings.

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The interactions between thiocarbamate herbicide, dimepiperate (S-(α, α-dimethylbenzyl) piperidine-1-carbothioate) and 7 compounds of herbicides including bensulfuron methyl and chlorsulfuron, oxyfluorfen and bifenox, clomeprop, pyributicarb, and pretilachlor applied to rice seedlings immediately after germination were studied under greenhouse conditions. Germinating seeds were grown hydroponically in Kasugai's nutrient solution containing dimepiperate and each herbicide, respectively. The growth responses to different combinations of these herbicides were determined at 7 days after application and sowing. Their interactions were evaluated based on Colby's and/or Isobole method.
The data indicated that there were antagonistic effects between dimepiperate and all the herbicides tested except for pretilachlor. Thus the safening effect of dimepiperate on the rice seedlings was confirmed as shown in Tables 1-6 and Fig. 1 and 2. An additive effect was noted only in the combination of dimepiperate and pretilachlor, indicated by the low percentage of recovery from growth inhibition (Table 7). The safening effect of dimepiperate was clearly demonstrated when the chemical was used with a wide range of other herbicides with different modes of action.

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Germination percentages of 52 kinds of weed seeds collected in 1990 and stored with control only of relative humidity were tested in December 1990 and May 1991. Promotional effect of germination by gibberellic acid (GA₃) was also tested. Seeds of twelve kinds of weed germinated well without GA₃ treatment in both tests, while eight kinds of seeds did not germinate well even if treated with GA₃. Many seeds germinated more in the May 1991 test than in the Dec. 1990 test, while the reverse was true of several others. GA₃ promoted the germination of seeds of many kinds, but the magnitude of the promotional effect differed between the two tests.

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