• Korean Journal of Weed Science
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• v.17 no.1
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• pp.73-79
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• 1997

Governments and industry have a growing interest in the harmonization of environmental test methods and risk assessment procedures. OECD are currently producing a set of harmonised test guidelines for studying the environmental fate and ecological effects of pesticides. FAO has published an environmental risk assessment procedure. This procedure, which is similar to those used in US and Europe, is based on calculating the ratio of the toxicity of a pesticide to indicator organisms to their level of exposure to the pesticide. The exposure depends on both the concentration of the pesticide and its bioavailability. Ratios which indicate a pesticide will not produce a harmful effect have been established using ecological field studies. Examples are presented for assessing the risk to aquatic ecosystems, earthworms and honeybees. Long-term field studies(up to 20 years) have also shown that pesticides can be used indefinitely without harming soil fertility. Herbicides can be used to avoid the ecologically damaging effects of using soil cultivations excessively for weed control.

• Korean Journal of Weed Science
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• v.4 no.1
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• pp.4-10
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• 1984

This experiment was conducted to determine the change in weed flora with season and cultivated crop and land. There are 44 species in 38 genera and 18 families, consisting of 22 annual, 11 biennial and 9 perennial weeds in uplands in Jeonbug Province. Digitaria sanguinalis Scopol. occurred with the highest frequency of 67.2% and in decreasing order Portulaca oleracea L., Chenopodium album L. and Erigeron canadensis L. followed. About 60% of total sites studied indicated Simpson`s index ranging from 0.20 to 0.50. The Simpson`s index decreased from 0.65 on June 8 to 0.15 on November 10. Dominant weed species were Alopecurus aequalis Sosbol, and Polygonum hydropiper Spach in double cropping paddy field, but D. sanguinalis and P. oleracea were the dominant species in uplands. In reclaimed uplands various weed species including, 4rtemisia asiatica Nakai occurred almost equally. Average Simpson`s index for six crops studied was 0.40 and irrespective of the crops being cultivated P. oleracea and D. sanguinalis were dominant weed species and Y. hydropiper, C. album, Exolus blitum Grenier and E. canadensis were sub-dominant.

• Korean Journal of Weed Science
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• v.4 no.1
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• pp.11-18
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• 1984

The effect of transplanting method of rice seedlings on weed occurrence was investigated at the Yeongnam Crop Experiment Station in 1983. Rice was transplanted by hand and machine and eleven common herbicides were applied. The greatest weeds were harvested from the plot that rice was not transplanted and more weeds encountered at machine transplanted plot than hand transplanted plot. The degree of weed suppression by rice plant itself was 50% for machine transplatning and 55% for hand transplanting, respectively. Simpson index and community dominance of weed species were the highest in hand transplanting and followed by machine transplanting and no rice plot in order. Rice grain yield was exponentially correlated with the amounts of weed occurrence and more yield loss exhibited at machine transplanting than hand transplanting in the same amount of weeds. In the herbicidal activity, most of herbicides performed better at hand transplanting than machine transplanting while the degree of difference between transplanting methods varied depend on herbicide used.

• Korean Journal of Weed Science
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• v.11 no.3
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• pp.224-228
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• 1991

This study was carried to know factors affecting emergence of major upland weeds in soil in order to get basic information on weed control methods. Firthy eight percent of weed seeds were distributed within soil surface to 10cm in soil and 2% of weed seeds were observed in 40~50cm soil layer in field. As planting depth was deeper, emergence of weeds became poor. However Capsella bursa-pastoris can emerge at soil surface. Amaranthus retroflexus, Amaranthus lividus, Porturaca oleracea, Chenopodium album, Solanum nigrum upto 3cm, Eleusine indica, Echinochloa crus-galli, Setaria viridis, Digitaria sanguinalis upto 7cm. Emergence of weeds was very poor in very acid soil but good in soil pH 5.5~6.0. However emergence of weed was not affected by pH 3.5~4.0 or above. Emergence of E. indica, C. bursa-pastoris, A. retroflexus, A. lividus, C. album, E. crus-galli, Solanum nigrum, and S. viridis was good in loam soil and P. oleranea, D. sanguinalis in sandy loam soil. Emergence of weed seeds was not affected by fertilization.

• Korean Journal of Weed Science
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• v.17 no.2
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• pp.139-146
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• 1997

The experiment was conducted at Gyeongbuk Provincial Rural Development Administration in 1996 to obtain basic information on weed ecology and effective weed control in direct-seeded rice fields under different seeding types and seeding times. A large number of upland weeds such as Echinochloa crus-galli, Digitaria sanguinalis, Capsella bursa-pastoris and Stetaria viridis etc occurred at early growth stage, while Eleocharis kuroguwai, Aneilema keisak and Cyperus serotinus dominated at late stage in dry seeded rice field. In wet seeded rice field, the dominance of E. crus-galli was lower and the occurrence of M. vaginalis and A. keisak were higher than in dry seeded field. Amount of weed occurrence in dry seeded field was 1.8 to 2.4 times greater than in wet seeded field and it increased with delaying seeding time. Increasing rate of weed occurrence through whole life cycle was the highest at 20 days after seeding (DAS) to 40 DAS, regardless of seeding types and seeding times. Simpson index in wet seeded field was higher than in dry seeded field and it gradually increased as growing of dominant species. For F-value test, it was recognized as statistical significant in seeding types, seeding times and interaction of two factors.

• Korean Journal of Weed Science
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• v.4 no.2
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• pp.135-142
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• 1984

To obtain the basic information for weed management in polder land, a colligated assessment on weed distribution and it`s plant sociological indices on Gyewha polder land were arranged. At the situation of assessment, the Gyewha polder land was reclaimed with aim with paddy-rice production. As a result of reclamation, the salinity of most soil samples were below 0.3%, and acidity ranged from pH 5.5 to 6.5. Total weed species were counted as much as 17 species (3 gramineae, 7 cyperucese, and 8 broad-leaved species), and a most dominant species, Scirpus maritimus, were succeeded with Monochoria v., Eleocharis a., and Cyperus d., etc. by reclamation. Declining of soil salinity and soil pH, the number of weed species, individuals, biomass, species diversity, evenness, sociability index were increased, but the population particularity was weaken in tendencies. By developing of reclamation, the weed species which is summer annual broad leaf, wind and water disseminating, and tussock formed species are increased instead of salt-resistant, perennial cyperus, and rhizomatous extending species.

• Korean Journal of Weed Science
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• v.4 no.2
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• pp.179-187
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• 1984

This experiment was carried out to clarify the effect of herbicide chlormethoxynil 7G, CNP 9G and butachlor 3.5/pyrazolate 6G on weed control and seedling growth in rice seedbed. Different quantities of the herbicides were applied as soil incorporation or surface broadcasting. At earlier sowing annual grasses such as Echinochlva spp. and Alopecurus spp. were dominated, but Cyperus spp. were dominated at later sowing. Weed suppression by herbicides was greater in soil incorporation than in broadcasting and chlormethoxynil 7G and CNP 9G application (30kg/ha) showed about 70% weed control, while butachlor 3.5/pyrazolate 6G (10-20kg/ha) showed 90 to 100% weed control. At lower rate of butachlor 3.5/pyrazolate 6G (10kg/ha) emergence ratio, healthy seedling ratio and relative growth rate of rice were higher, and phytotoxicity was lower than in the others.

• Korean Journal of Weed Science
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• v.13 no.2
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• pp.114-121
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• 1993

Differences in need occurrence and competition were investigated among five types of rice(Oryza sativa L.) cultivation. Dry weights of weeds in between transplanting and/or seeding and heading date showed in the decreasing order of dry direct-seeded, flood direct-seeded, machine transplanting with 10-day-old seedling, machine transplanting with 30-day-old seedling, and conventional hand transplanting. A similar trend was obtained with application of weedy followed by weed-free. Weed-free periods allowed to decrease by 20% dry weight of rice were 3 weeks after transplanting(WAT) in transplanting cultivations, 5 weeks after seeding(WAS) in wet direct-seeded rice, and 7-8 WAS in dry direct-seeded rice. On the other hand, weedy periods as determined by the same criterion were 9 WAT in conventional hand transplanting and machine transplanting with 30-day-old seedling, 7 WAT in machine transplanting with 10-day-old seedling, 8 WAS in dry direct-seeded rice, and 6 WAS in flood direct-seeded rice.

• Korean Journal of Weed Science
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• v.13 no.2
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• pp.159-163
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• 1993

This research was conducted at the Crop Experiment Station to determine the changes of weed flora under direct seeded rice cultivation in dry paddy field from 1989 to 1992 and to establish an effective weed control strategy in direct seeded rice cultivation. With the continuous rice growing under direct seeded rice cultivation in dry paddy field, there were more occurrence in grasses and annual weeds while broadleaf and perennial weeds were diminished. The predominant weeds were aquatic weeds such as Eleocharis kuroguwai, Echinochloa crusgalli, and Monochoria vaginalis in machine transplanted rice paddy field while there were predominant of semi aquatic weed species such as E. crusgalli, Digitaria sanguinalis, Bidens tripartita, Aeschynomene indica, and Arthraxon hispidus in continuous direct seeded rice cultivation in dry paddy condition. Based on the vegetative analysis of weeds in terms of simpson index and community dominance, there was more distribution of weed species in direct seeded rice cultivation on dry paddy condition while only distributed with 1-2 weed species in machine transplanted rice paddy field. In similarity coefficient, there was a gradual increase up to 67% of weeds with the continuous direct seeded rice cultivation in dry paddy condition for 4 years starting from 41% of similarity coefficient.

• Korean Journal of Weed Science
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• v.3 no.2
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• pp.120-128
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• 1983

The nationwide survey of weed population covering 1,800 wheat and barley fields in 60 Cities and Guns all around Korea was conducted in December of 1982 and March-April of 1983. In this survey result, two species of gresses and 35 species of broadleaves were identified, and among them 36 and 29 species were found in the wheat and barley fields of upland and paddy, respectively. In the scope of weed life cycle, biennials were more dominant than perennials and annuals in these fields. The most dominant weed species in upland fields were Stellaria media, Cyrillus and Alopecurus aequalis Sobol var. amurensis Ohwi while those in paddy fields were Stellaria alsine Grimm. var. undulata Ohwi and Alopecurus aequalis Sobol var. amurensis Ohwi. In addition, the more weeds were observed in the conventional row seeding method than in other seeding methods including drill seeding and also in no-tillage than in tillage method. In the other hand, the successive use of herbicide for several years greatly influenced the pattern of weed occurrence; broadleaved weeds increased and grasses decreased with the successive use of herbicides.