The author studied the physiological and ecological characteristics of Scirpus weeds, so-called “hotarui”, Scirpus juncoides Roxb. var. hotarui Ohwi, S. juncoides Roxb. var. ohwianus T. Koyama and S. wallichii Nees, then identified the dominant species of Scirpus weeds in paddy fields and determined the cause of the dominance of the species. Based on these data, the author attempted to establish an effective control method for this noxious weed.
1. The numbers of chromosomes in the pollen mother cells of S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii were 22, 37 and 36 respectively.
Although S. juncoides var. ohwianus was identified in all the seed samples collected from 17 research stations in 15 prefectures, S. juncoides var. hotarui was not detected at all. S. wallichii and S. hondoensis Ohwi var. leiocarpus Ohwi was identified in 3 and 1 seed samples respectively at very low rates.
Scirpus plants S. juncoides var. hotarui were never observed in paddy fields where almost all Scirpus plants consisted of S. juncoides var. ohwianus and a few rest was S. wallichii.
2. Seeds of the three species which overwintered under submerged conditions showed higher emergence rates than those in soils under damp and upland conditions in a greenhouse.
The temperatures at which S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii emerged were in the range of 25-35°C, 15-35°C and 20-40°C, respectively.
The emergence rates of S. juncoides var. hotarui and S. wallichii were reduced by covering with soil at depths of more than 1 and 1.5cm respectively, but those of S. juncoides var. ohwianus were not reduced by covering with soil at a depth of 3cm.
S. juncoides var. hotarui and S. juncoides var. ohwianus sown in soils containing more than 75% of water in MWC base showed more than 70% emergence, but S. wallichii gave 94% emergence in soil containing 40% of water in MWC.
3. When the seeds were sown in turn from April 12th to July 17th, the growth of S. juncoides var. ohwianus was faster than that of the other two species at any time.
The growth of the three species was delayed almost linearly with the increase in shade intensity. But the decrease in the stem number of S. juncoides var. ohwianus with shading was less pronounced than that of the other two species under shaded conditions, compared with the control.
4. Under natural day length conditions, the time of heading and flowering of S. juncoides var. hotarui was the most delayed.
The heading of S. juncoides var. hotarui and S. wallichii was remarkably delayed or inhibited by shading whereas that of S. juncoides var. ohwianus was also delayed but to a lesser extent than that of the other two species.
The three species cultivated under natural conditions regrew after their aerial parts were cut off on the 25th of October. Although 50% of the regrown plants of S. juncoides var. ohwianus headed, none of the other species did.
The mean numbers of seeds per stem of S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii were 93, 317 and 267 respectively.
5. S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii overwintered regardless of soil moisture content.
When the weights of overwintering stumps of S. juncoides var. hotarui and S. juncoides var. ohwianus were reduced to less than 32% of the initial weight by drying

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The purpose of this experiment was to evaluate the effect of the application to soil of herbicides in drained paddy fields in which naked barley being cultivated and where Stellaria alsine GRIMM var. undulate OHWI grew actively. Effects of single -or combined- applications to soil of several herbicides on the weeding efficacy and growth and yield of naked barley were investigated. The results obtained are as follows.
1. Trifluralin was more effective in controlling S. alsine, but less effective in controlling gramineous weeds than the combination of benthiocarb·prometryne. The combined application of trifluralin+prometryne and trifluraline+simazine was more effective in controlling gramineous weeds than the single application of trifluralin. Yield of naked barley was not affected by the treatment with these herbicides.
2. In the case of soil application performed immediately after seedling, photosynthesis and growth of barley were remarkably decreased by the application of photosynthetic inhibitors sach as simazine, prometryne and diuron, and slightly decreased by the application of chrolopropham and dichrobenil, but not by trifluralin.
3. Photosynthesis was decreased by the combined application of trifluralin+simazine, trifluralin+prometryne and trifluralin+diuron at early growth stages in barley, but the inhibition was removed as barley plant grew. Photosynthesis and growth of barley were markedly inhibited by the combined application of trifluralin+simazine.
4. The combined application of trifluralin+prometryne was effective in controlling S. alsine and gramineous weeds in paddy fields.

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The slectivity of both foliar-and root-applied propanil was studied among five gramineous plant species. In both applications, finger millet (Eleusine coracana (L.) GAERTN.) showed considerable tolerance to propanil, although it was less tolerant than rice (Oryza sativa (L.) cv. Nihonbare). Large crabgrass (Digitaria ciliaris (RETZ.) KOELER), goose grass (Eleusine indica (L.) GAERTN.) and barnyardgrass (Echinochloa oryzicola VASING.) were found susceptible to propanil. The mechanism of tolerance of finger millet to the herbicide was studied. Metabolic change of ¹⁴C-propanil in roots and shoots of rice was much greater than in finger millet and barnyardgrass, and most of the ¹⁴C-propanil actually remained unchanged in the latter two plants. Finger millet and barnyardgrass hydrolyzed no propanil at all, while rice did. Substrate specificity of the enzyme was surveyed and only rice plant hydrolyzed propionanilide, propanil and 2, 3-dichloropropionanilide. All three plants have arylacylamidase II activity. Differences in rates of absorption of ¹⁴C-propanil by shoots were in the following order: barnyardgrass>rice>finger millet. The rate of translocation of ¹⁴C-propanil from roots to shoots of finger millet was comparatively less than that of rice and barnyardgrass.
It is concluded that the tolerance of finger millet to propanil is not due to the hydrolytic degradation of the substance, but that the lower accumulation of the chemical in shoots resulting from its lower rate of absorption by the shoots or the lower amount translocated from roots to shoots may contribute to this tolerance.

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Optimum time for glyphosate application, to achieve both a good control of horsenettle and better conditions for pasture renovation by sod-seeding, was determined during the period 1983 to 1984. Three application times were evaluated in plants subjected to treading and those without treading.
The results obtained were as follows:
1) The best control of horsenettle was obtained by the application of glyphosate on August 30, when the plants were at the late bloom or fruiting stage. Glyphosate was more effective in uninjured plants than in those damaged by treading (Fig. 2, Table 1).
2) For pasture renovation with sod-seeding orchardgrass, the application of glyphosate on August 30 was also superior to the other treatments. Though there remained two weeks till sod-seeding time, glyphosate applied at a rate of 4.1kg/ha could well suppress the vegetation including horsenettle and contribute to the increase of productivity of forage (Table 2).
3) These results suggest that late August application is the most suitable for the use of glyphosate for sod-seeding renovation of pasture heavily infested with horsenettle.

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Four-hundred and seventy-seven, and 150 culms of A. repens were collected from cultivated land in the Tokachi district in Hokkaido in early to middle August 1980, and from an abandon field at Obihiro in early August 1981, respectively. Seeds per culm, morphological characters of inflorescences and germination rate were examined.
1) Sixty-four per cent of the total culms bore 60 to 120 florets. A larger number of florets were formed on the longer culms or spikes (Fig. 1).
2) Culms with 0, 1 to 10 and more than 10 seeds accounted for 37, 33 and 30%, respectively (Fig. 1).
3) Germination rate was 77 and 63% in samples collected from winter wheat and corn fields, respectively (Fig. 2). Viable seeds per culm were estimated to be 15.7 and 7.4, respectively, and 8.9 as a total mean (Table 1).
4) Awn length largely varied among the culms, and in 52 and 23% of them awn length was less than 1mm and more than 3mm, respectively (Fig. 3).
5) Populations which showed variable awn length tended to have more seeds (Table 2). In addition, samples taken from the field adjacent to an abandoned field had more seeds per culm than those from inner sites (Fig. 4).

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Effects of five nitrogen levels (0, 5.0, 10.5, 21.0kg per 10 acres) on the growth and seed production of Paspalum urvillei Steud., an agressive sugarcane field weed, were investigated.
1. Plant height increased rapidly at all nitrogen levels throughout the vegetative growth period with a subsequent decrease at 0 level. Plant height at the end of the experiment was the lowest at 0 level in remarkable contrast with values at other levels.
2. Tiller number, leaf area and top dry matter weight increased appreciably with increasing nitrogen level. No substantial variations were observed in maximum root length and root dry matter weight.
3. Differences in nitrogen level had almost no effect on days to heading.
4. Panicle number and panicle weight increased with increasing nitrogen level. Percentage of productive tillers decreased rapidly with the increase of the nitrogen level.
5. In the characters associated with vegetative growth, the coefficient of variation was large for the tiller number and top dry matter weight, especially for the former character. In the characters associated with reproductive growth, the variation was high for the panicle number per plant and panicle weight per plant. The variation in 1, 000 seed weight and days to heading was extremely low.
6. In this weed, heavy application of nitrogen in a field may result in the excessive growth of the top part and subsequently it may cause shading on crop.

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Effects of shading (relative light intensity: RLI 100%, 80%, 70%, 50% and 30% of natural sunlight) on growth and seed production of Paspalum urvillei Steud., a perennial weed, were investigated and the following results were obtained.
1. Plant height increased with decreasing relative light intensity. Tiller number decreased at higher RLIs.
2. Total dry matter weight (top dry matter weight plus root dry matter weight) and top dry matter weight attained high values at 70% and 80% RLIs. These results may be attributed to the increases in leaf area and tiller number.
3. In the characters associated with seed production all but 1, 000 seed weight increased at 80% RLI, resulting in maximum seed production at this RLI.
4. In this weed, both growth and seed production were enhanced under lower shading conditions, indicating that control programs should be crried out in advance of the time when the crop provides sufficient shade cover for the weed.

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Effects of soil moisture on the growth and seed production of Paspalum urvillei Steud., a perennia lgrass weed in sugarcan fields, were investigated under 20, 32, 58 and 64% (w/w) soil moisture conditions. The following results were obtained:
1. Plant height increased the with the increase of the soil moisture level. Plant height in the maturity period was maximum at 64% level and minimum at 20% level. Approximately the same results were obtained for the tiller numcer.
2. Among the characters associated with productivity, top dry matter weight, root dry matter weight and total matter weight (top dry matter weight plus root dry matter weight) were the largest at 64% level and the smallest at 32% level.
3. Similar results were obtained for the characters associated with seed production, namely, panicle number per plant, panicle weight per plant, panicle weight and 1, 000 seed weight.
4. Percentage of productive tillers was the highest at 64% level and the lowest at 32% level.
5. In the characters associated with weight growth increment, phenotypic plasticity was highest for the top dry matter weight. In the characters associated with seed production, phenotypic plasticity was highest for the panicle number per plant and lowest for 1, 000 seed weight.
6. In this weed, growth and seed production are enhanced especially in areas where high levels of soil moisture occur and effective control is therefore difficult. This fact should be taken into due consideration in any program for the cultivation of sugarcane in such areas.

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