In order to analyse the properties of bromobutide [(R, S)-2-bromo-N-(α, α-dimethylbenzyl)-3, 3-dimethylbutyramide] as a paddy field herbicide, efficacy against paddy weeds and injurious effect on rice were investigated under greenhouse and outdoor conditions. The results obtained are summarized as follows.
1. Bromobutide did not inhibit the germination of weeds, but strongly inhibited the growth of weeds after emergence.
Bromobutide applied at the post-emergence stage of weeds also strongly inhibited the growth of foliar and underground parts of weeds such as Sagittaria pygmaea Miq. and Cyperus serotinus Rottb. (Fig. 2 and 3).
2. Under greenhouse conditions, bromobutide applied at the pre-emergence or very early post-emergence stages of weeds, at doses of less than 20g/a, controlled effectively annual weeds such as Echinochloa oryzicola Vasing., Monochoria vaginalis (Burm. f.) Presl, Lindernia pyxidaria L., Rotala indica (Willd.) Koehne and perennial weeds such as Scirpus juncoides Roxb. subsp. juncoides Roxb., Eleocharis acicularis (L.) Roem. et Schult. var. longiseta Sven., C. serotinus, Eleocharis kuroguwai Ohwi and S. pygmaea.
Bromobutide was especially effective against S. juncoides, and it controlled the weed even at doses as low as 1.25g/a (Table 1).
3. Based on the results of tests using concrete pots placed outdoors for the evaluation of the practical performance of bromobutide, 6% granules of bromobutide at doses of 12-24 a. i. g/a controlled effectively Cyperaceae weeds such as S. juncoides and C. serotinus. However the effect against E. oryzicola and S. pygmaea varied with the doses or time of application, and the effect against broadleaved-weeds was not satisfactory.
Granular combinations of bromobutide+chlomethoxynil, 6+5% and bromobutide+bifenox, 6+5% controlled effectively all the weeds examined (Table 2).
4. Possible injury of bromobutide to transplanted rice was examined using 1/5, 000 a Wagner pots.
Though bromobutide slightly inhibited the growth of young rice seedlings when applied at relatively high doses of 36g/a, it did not display any injurious effect when applied at lower doses or when the leaf stage of the rice seedlings exceeded 3.5 (Table 3).

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Two Asp-related iridoidglucosides, compounds A and B were isolated from the dormant seeds of catchweed. By chemical analysis, compound A was identified as asperulosidic acid which was derived from Asp through the cleavage of a lactone ring, and compound B as deacetyl asperulosidic acid produced through the deacetylation of asperulosidic acid. Asperulosidic acid inhibited the seed germination and growth of seedlings of large crabgrass and alfalfa to the same degree as Asp, but did not inhibit white clover, while deacetyl asperulosidic acid showed lower inhibitory effect on the tested plants than Asp and asperulosidic acid. Furthermore, asperulosidic acid showed similar inhibitory activity to Asp on the germination of catchweed seeds themselves. Since these compounds were only detected in the exudate obtained from the seed coat of catchweed seeds, inhibition of the germination and growth of lettuce placed together with catchweed seeds may be due to iridoidglucosides liberated from the latter seeds which have been soaked in water.

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The nature and extent of competition between sugarcane and Bidens were investigated. Cane was grown by the conventional cultural practices either alone or in competition with Bidens and the weed was removed at an interval of from 30-60 days after seeding to determine the effect of prolonged weeding on growth of the crop.
For cane, the relative light intensity at 30 days after planting was 90% in the middle of the hills and 100% in the middle of the groove between the rows. The relative light intensity then decreased sharply, the results at 120 days after planting being 2.5% in the middle of the hills and 11% in the middle of the groove. The growth of Bidens main stem length was considerably less than that of cane plant length until up to 30 days after seeding but this difference became less marked at subsequent stages of growth. The growth of cane plant length was further suppressed as the period of weeding was prolonged.
Cane leaf area, leaf blade dry weight and specific leaf area were largest in the pure plot (weedfree plot) and decreased in the mixed plots (plot with weed competition) as the period of weeding was prolonged. Main stalk leaf number and tiller number were large in the pure plot throughout the period of growth and became smaller in the mixed plots as the period of weeding was prolonged.
Main stalk weight and tillering stalk weight, the major yield-controlling elements, were largest in the pure plot and decreased in the mixed plots as the period of weeding was prolonged. Weight values in the mixed plot left unweeded for 120 days after planting were as low as about one-fifth and about one-thirty-eighth, respectively, of the pure plot results.
The severity of competition from Bidens was clearly indicated by the fact that the growth of cane was suppressed more as the period of weeding was prolonged and suppression by the weed reached nearly 80% in the plot left unweeded for 120 days after seeding. In contrast, suppression by the crop was only 10% at 60 days after planting with a further decrease to about 4% in the plot left unweeded for 120 days after planting.
Since Bidens damage becomes serious at 60 days after emergence, it is recommended that the weed be removed earlier (at least within 45 days of emergence) in order to prevent cane yield reductions.

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With a view to identifying new herbicide models in natural sources and also to investigating allelopathy phenomena among higher plants, the mode of action and biological activity of allelochemicals and herbicides with a similar chemical structure were compared
The combination of gallic acid (3, 4, 5-trihydroxybenzoic acid, an allelochemical from Eucalyptus camadulensis) and 2, 3, 6-TBA (2, 3, 6-trichlorobenzoic acid, a benzoic acid herbicide) was investigated.
The auxin activity was higher in 2, 3, 6-TBA than in gallic acid (Table 4). This activity was different from that of a simple acid growth inhibitor (Table 5). The inhibitory activity of gallic acid on the growth of rice plant (Oryza sativa L.) and barnyardgrass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi) was 1/50-1/100 times as high as that of 2, 3, 6-TBA and this activity was proportional to the auxin activity (Fig. 2).
The auxin activity of gallic acid was compared with that of 2, 3, 6-TBA by applying the elongation test of Avena coleoptile segments, elongation test of pea hypocotyl segments, curvature test of slit pea (pea test) and extension test on the lamina joint of rice plant. The results of these tests suggested that although the mechanism of growth inhibition of both substances could be ascribed to auxin activity, the activity of gallic acid was weaker than that of 2, 3, 6-TBA.

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The infestation of R. obtusifolius (Ezonogishigishi) and distribution pattern of its individual plants were investigated in sown grasslands in eastern Hokkaido during 1983 to 1985.
1) About 60% of sown grasslands were infested with R. obtusifolius, one -third of them seriously. High infestation of R. longifolius (Nodaio) occurred only in peat soil areas.
2) The occurrence of R. obtusifolius was positively associated with that of annual arable weeds such as Capsella bursa-pastoris (Nazuna), Chenopodium album (Shiroza), Rorippa islandica (Sukashita-goboo), Polygonum longisetum (Inutade) and Stellaria media (Hakobe).
3) There was no significant difference of soil pH and nitrogen content on grasslands irrespective of the infestation of R. obtusifolius.
4) Individual plants of R. obtusifolius distributed unevenly in sown grasslands with a L-type distribution.
5) The distribution pattern of dry matter weight per plant was approximately logarithmnormal with a high proportion of smaller plants.

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