• Korean Journal of Weed Science
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• v.31 no.4
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• pp.340-347
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• 2011

This study was conducted to predict the rice yield loss and to determine the economic threshold levels for direct-seeding flooded rice cultivation from competition to the most serious weeds, Sagittaria trifolia L. and Bidens frondosa L. The rice yield loss models of S. trifolia and B. frondosa were predicted as Y = 497.0/(1+0.003760x), $R^2$=0.869 and Y = 486.0/(1+0.007612x), $R^2$ = 0.887, respectively. In comparison of the competitiveness represented by parameter ${\beta}$, it was 0.003760 in S. trifolia and 0.007612 in B. frondosa, respectively. Economic thresholds calculated using Cousens' equation was negatively related with the competitiveness of weed. The economic thresholds of S. trifolia and B. frondosa were 7.6 and 3.9 plants per $m^2$, respectively.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.28 no.3
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• pp.310-318
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• 1983

Four methods of vegetation analysis were compared to determine the most suitable method to use in transplanted rice. The highest number of weed species, 14 was obtained with the list quadrat method while the least number, 8 was obtained with the line intercept method. The clip quadrat method tended to overestimate weed species with a low moisture content such as Sagittaria trifolia L. and Ludwigia prostrata Roxb while for the list quadrat method, weed species with a high moisture content such as Sagittaria pygmaea Miq. and Monochoria vaginalis (Burm. f) Pres 1 were overestimated. With the line intercept method, weed species having conspicuous leaf blades such as S. trifolia and Potamogeton distinctus Benn. were dominant. Of the methods tested, the line intercept method was the least desirable because it accounted for the least number of weed species. Any of the others could be use for vegetation analysis without any significant problems arising. However, preference was given to the point quadrat method because of the ease of measurement. It was also less tedious and less time consuming than the other methods.

• Korean Journal of Weed Science
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• v.32 no.1
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• pp.52-56
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• 2012

The occurrence of sulfonylurea-resistant weeds has recently increased in Korea. A survey was performed to investigate major paddy field weeds and frequently used herbicides in Gangwon province, Korea in order to establish a system to efficiently control herbicide-resistant weeds. The dominant paddy field weeds included Monochoria vaginalis (14%), Sagittaria trifolia (14%), Scirpus juncoides (13%), and Echinochloa spp. (13%), and the most widely used herbicides were oxadiazon 12% EC (27%), butachlor 5% GR (20%), oxadiargyl 1.7% EC (16%), and benzobicyclon+imazosulfuron+pyriminobac-methyl 6.1% SC (14%) in Gangwon province, Korea. Many paddy rice growers considered Scirpus juncoides, S. trifolia, Echinochloa spp. and M. vaginalis as herbicide-resistant weeds. An extensive research deserves to be conducted to monitor occurrence of herbicide-resistant paddy weeds in Gangwon province, Korea.

• Weed & Turfgrass Science
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• v.3 no.1
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• pp.6-12
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• 2014

The survey of weed occurrence was conducted to identify problem weed species in the paddy field. The 320 sites of the 13 regions in Gyeongbuk Province were investigated from June to July, 2013. In the whole region, 51 weed species were identified including 34 annuals and 17 perennials. The highest importance value of annual weed and perennial was dominant 88.4 and 48.7%, in Gumi region, respectively. The most dominant weed species in paddy fields of Gyeongbuk Province were Monochoria vaginalis var. plantaginea (10.80%), followed by Lemna paucicostata (10.74%), Bidens tripartite (8.77%), Echinochloa oryzoides (7.17%), and Scirpus juncoides (6.20%). The similarity of paddy weeds in 13 regions observed through TWINSPAN analysis was distinguished by Ludwigia prostrata, Scirpus juncoides, Lindernia dubia, Polygonum aviculare, and Alopecurus aequalis var. amurensis. The weed species, Ludwigia prostrata, was divided into the four regions, Gyeongju, Gumi(direct seeding cultivation), Youngcheon and Euiseong and ten regions, Gumi, Bonghwa, Sanju, Goryung, Youngdeog, Pohang, Sanju, Andong, Yecheon, and Cheongdo.

• YAKHAK HOEJI
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• v.42 no.2
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• pp.140-143
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• 1998

From the methanol extract of the whole part of Sagittaria trifolia ergosterol peroxide, icariside D2. Thalictoside and 4-nitrophenyl $\{beta}$-D-glucopyranoside wer e isolated and their structures were identified by the physico-chemical and spectral data. This is the first report of these compounds from S. trifolia.

• Korean journal of applied entomology
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• v.31 no.2
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• pp.139-143
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• 1992

Feeding plants of rice water weevil(RWW) adult and larvae were observed. Thirteen families including 104 species were found as host plants of RWW adult, and 74 species of them were newly identified as its host. Thmedia triandra var. japonica, Luzula capitata, Agropyron tsukushiense var. ransiens, and Zoysiama crostachya were most favorable hosts of adult RWW. Host plants for larvae were 9 species of weeds including Cperus nipponicus, Eleccharis kuroguwa, Sagittaria trifolia, and Claviceps purpurea in the rice paddy fields.

• Korean Journal of Weed Science
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• v.12 no.4
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• pp.317-334
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• 1992

Weed flora and floristic composition were reviewed in lowland rice field and upland crop area. For lowland rice field weed flora was not much changed since 1971. About 29 weed species belonged to 18 families were occurred. However, floristic composition of dominant weed species has greatly changed mainly due to introduction of herbicides. The predominant weed species in 1971 when herbicide was not used were Rotala indica, Eleocharis acicularis, Monochoria vaginalis, Echinochloa crus-galli, while these for in 1991 were Eleocharis kuroguwai, Sagittaria pygmaea, S. trifolia, Echinochloa crus-galli and M, vaginalis, respectively. In 1981 weed survey, E. crus-galli was no longer troblesome weed. However, this species became important again thereafter by introduction of herbicide mixtures with pyrazolate, bensulfuron-methyl or pyrazosulfuronethyl. For upland crop area, 216 weed species belonged to 46 families were recorded. One hundred and sixtyfive of these were grown in winter crop area while 189 weed species occurred in summer crop area, respectively. Among these, 138 weed species were grown in both crop seasons. In general, summer crops had less number of weed species compared to winter crops. Even though the dominant weed species varied by crop the most common weeds were Chenopodium album, Alopecunrs aqualis, Stellaria alsine and S, media for winter crops and Digitaria sanguinalis, Portulaca oleracea, Chenopodium album and Acalypha australis for summer crops, respectively.

• Weed & Turfgrass Science
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• v.7 no.3
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• pp.201-208
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• 2018

This study was conducted to investigate the occurrence and distribution of herbicide resistant weeds at rice fields in Chungnam province of Korea in 2017. Herbicide-resistant weeds occurred in 64,782 ha, which comprise 47.0% of the total paddy field area of Chungnam province. The infested area of herbicide resistant weeds was estimated in Seosan-si (11.9%), Nonsan-si (11.1%), Dangjin-si (10.9%), Boryeong-si (9.2%) and Asan-si (7.8%). The most dominant herbicide resistant weeds in rice fields were Monochoria vaginalis, followed by Lindernia dubia, Schoenoplectus juncoides, Echinochloa oryzicola, Cyperus difformis and Sagittaria trifolia. Herbicide resistant M. vaginalis, L. dubia, and S. juncoides occurred throughout Chungnam province, and herbicide resistant S. trifolia was only found in Dangjin-si. Compared with the 2011 survey, the infested area of herbicide-resistant weeds decreased, but the incidence rates were similar. The herbicide rotation with different modes of actions across growing seasons is recommended to control herbicide-resistant weeds in the infested fields. It is necessary to monitor herbicide resistance regularly and conduct integrated herbicide resistance management in this area.

• Korean Journal of Weed Science
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• v.32 no.2
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• pp.127-132
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• 2012

Field survey on the weed occurrence and the use of herbicides was carried out targeting 214 rice cultivating farmers at Gyeongsangbuk-do. 96.2% of farmers did machine planting in late May and this is 68.0% of total cultivating area. Spring plowing was first with 54.6%, followed by spring-fall and fall plowing with 24.8% and 15.0%, respectively. 75% of the farmers treated herbicide twice. 57.5% of them treated herbicide before transplanting and treated at post-emergence again. In case of only application, 84% of the farmers treated herbicide before transplanting. Twenty-three species were occurred at Gyeongsangbuk-do and Echinochloa spp. was the most dominant with 20.8%, Sagittaria trifolia was second with 10.4%, followed by Monochoria vaginalis and Sagittaria pygmaea with 9.9% and 9.7%, respectively. Sagittaria pygmaea was the most difficult to control followed by Echinochloa spp., M. vaginalis, and S. trifolia.

• FLOWER RESEARCH JOURNAL
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• v.16 no.1
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• pp.63-70
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• 2008

This experiment was conducted to acquire the basic data necessary for the artificial pond greening. Eighty four hydrophytes collected from 11 domestic small ponds and a farm were used in this experiment. The size of the artificial pond used was $6m{\times}3m{\times}1.5m(length{\times}width{\times}depth)$. Twelve months after planting, species were selected for their high ornamental values and tissue contents of N and P in each month. Tissue contents of N in Trapha nantan, Nymphoides indica, Nymphaea hybrid, and Murdannia keisak were high. Tissue contents of P in Monochoria vaginalis and Murdannia keisak were also high. The pH of artificial pond stabilized at a 6.8~7.6 range from May 2005 to March 2007. The EC was low in summer and high in autumn. From April to October, 5, 19, 23, 32, 31, 28, and 26 species, respectively, were selected for artificial pond greening. One year after planting, vegetation changed from 78 species (Potamogeton octqandrus, Salvinia natans, Potamogeton malaianus, etc.) to 38 species (Scirpus tarbernaemontani, Scirpus karuizawensis, Scirpus triqueter, etc.). Species diversity in the artificial pond was as follows, indicating it being a stabilized artificial pond; 38 species, 1,437 total number of plants, species richness index of 11.72, and maximum diversity index of 0.97.