1. The purpose of the present study is to investigate and set up a phytosociological classification weed communities occurring in sugarcane fields throughout the Ryukyu Islands. This report presents the data obtained for Ishigaki Island.
2. Thirty-one (31) parameters relating to vegetation were assembled the tabulated using the method of Zurich-Montpellier. The following vegetation units were identified.
Veronica javanica-Anagallidetum coeruleae MIYAWAKI 1969
A Sub-association of Amaranthus spinosus.
a: Variant cf Arenaria serpyllifolia.
b: Typical variant.
B: Typical sub-association.
C: Sub-association of Centella asiatica.
c: Typical variant.
d: Variant of Paspalum conjugatum.
3. Variant of Arenaria serpyllifolia and typical variant of the sub-association in the Amaranthus spinosus occur in well-managed newly planted fields, except that the quality of management is higher for the former. Typical variant of the sub-association of Amaranthus spinosus and variant of Paspalum conjugatum in the sub-association of Centella asiatica occur both in poorly managed newly planted and ratooned fields.

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Two Echinochloa species, E. oryzicola and E. crus-galli var. crus-galli were observed in a paddy field of the Shonai-district. The physiological and ecological properties of the two species were compared. E. oryzicola showed a longer life-span under flooded soil conditions and produced heavier seeds with shorter awn, while E. crus-galli var. crus-galli showed a higher ability of dispersion, earlier maturing, higher reproduction rate and shorter life-span. The utilization of Emmalocera sp. for the biological control of the two species was considered to be more effective in the case of E. oryzicola than in E. crus-galli var. crus-galli, for seed germination of E. oryzicola did not occur at the same time in contrast with the other species. The stage at which the transition from the vegetative to the reproductive phase took place differed between the two species, i. e. 9th leaf stage for E. crus-galli var. crus-galli and 11th for E. oryzicola. Consequently since it is considered that the damage would be more severe and last longer in the latter species, it is suggested that Emmalocera sp. could be utilized for the biological control of E. oryzicola after the first spraying of herbicide.

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DPX-F5384, methyl 2-[[[[[(4, 6-dimethox-pyrimidin-2-yl) amino] carbonyl] amino] sulfonyl]methyl]benzoate and several analogs were examined for herbicidal activities, crop safety, and selectivity.
(1) Both DPX-F5384 and DPX-T6375 which have substitutents of 2-CO₂CH₃ were tested in petri dishes to examine their effect during early growth stage of rice, Brassica pekinensis and Sagittaria pygmaea. The results indicated that DPX-F5384 has the highest selectivity between rice and other plants. DPX-T6357 provided little selectivity.
(2) DPX-F5384 and the analogs were tested for herbicidal activity and crop safety under paddy rice conditions. DPX-W4515, DPX-T6375, DPX-W4189, and DPX-T6376, all with phenyl moiety, exhibited very high weed control activity, but caused severe phytotoxicity on transplanted rice exhibiting little selectivity between rice and weeds. DPX-F5384, with 2-CO₂CH₃ substituted benzyl moiety, was highly active, 2-Cl substituted DPX-F5390 had very low activity. In contrast to the benzyl type derivatives, DPX-R5582, with 2-Cl substituted phenoxy, had considerably high activity.
Among the sulfonylurea compounds exa mined, DPX-F5384 proved to have sufficient crop safety for rice. DPX-R5582 was relatively safe to rice but its safety margin was not broad enough. In addition, DPX-R5582 was not particularly active on Scirpus juncoides, one of the major weeds in rice paddies. DPX-F5384 was the best compound based on its high weed control activity and selective safety to rice.

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DPX-F5384, methyl 2-[[[[[(4, 6-dimethoxypyrimidin-2-yl) amino] carbonyl] amino] sulfonyl] methyl benzoate was studied for biological activity, selectivity and mobility in paddy soil. At 25g a. i./ha, the compound showed excellent control of annual broadleaf weeds and sedges in pot tests. Perennial weeds such as Eleocharis acicularis, Scirpus juncoides, Sagittaria pygmaea, and Cyperus serotinus were controlled at 50g a. i./ha, however, control of Echinochloa oryzicola was not acceptable even at 200g a. i./ha.
Rice plants were tolerant to DPX-F5384. Slight growth retardation was observed with the treatment at 200g a. i./ha, but rice plants recovered rapidly.
The results of sensitivity in comparison with broadleaf crops indicated that rice is more highly tolerant to DPX-F5384 than Chinese cabbage or spinach.
Mobility of the compound in paddy soil was relatively limited (2cm) and similar to that of butachlor.

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Physiological and ecological characteristics of Bidens pilosa L. var. radiata Scherff. a serious, dimorphic perennial weed of Compositae occurring in sugarcane fields, were investigated in an effort to establish effective measures of control. This first run of experiments were carried out for both long and short achenes. The results are as follows:
1. In achenes which were air-dried indoors for a period of 10 days after collecion and then stored in a desiccator for a period of 20 days at room temperature, germination under light conditions was enhanced at 25-35°C and suppressed at 10°C. Germination under dark conditions was suppressed at 30-40°C and enhanced at 10-20°C. Germination percentage was higher in long achenes than in short achenes (Fig. 3).
2. In achenes which were air-dried indoors for a period of 10 days after collection and then stored in a desiccator for a period of 9 months at room temperature, the same results as those described above were obtained for germination under light conditions. The difference was that germination under dark conditions was suppressed slightly at 10°C and approximately the same results as under light conditions were obtained for germination at 20°C (Fig. 4).
3. Light wavelength had a distinct effect on germination. Exposure to green light severely suppressed germination of both long and short achenes (Fig. 5).
4. In both long and short achenes, emergence decreased with the increase of soil cover depth. At a depth of 10cm no emergence was observed (Fig. 6).
5. In both long and short achenes, the germination percentage increased at higher moisture intensities. At a relative humidity of 37.5%, no germination was observed (Fig. 7).

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