• KOREAN JOURNAL OF CROP SCIENCE
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• v.23 no.2
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• pp.150-153
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• 1978

A study was conducted to determine the critical period of weed-free maintenance required to produce maximum soybean yields. Leaf area index(LAI). crop growth rate (CGR), and number of pods per plant were increased with extended weed-free maintenance period. Consequently, maximum soybean yields were obtained when weeds were controlled for more than six weeks, but a relatively high level of ;soybean production was attained with only two weeks of weed free maintenance.

• Korean Journal of Weed Science
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• v.14 no.3
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• pp.192-198
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• 1994

Zeaenol isolated from the culture filtrate of a fungal weed pathogen Drechslera portulacae, which causes necrosis on the leaves and stem of purslane (Portulaca oleracea). Its structure was determined by single-crystal x-ray diffraction method together with assignments of $^1H$ and $^{13}C$-NMR experiments. Zeaenol inhibited root length of Echinochloa crus-galli and Abutilon avicennae by 22.8% and 54.8% at $3{\times}10^{-6}M$, respectively.

• Korean Journal of Weed Science
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• v.17 no.3
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• pp.295-302
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• 1997

The study conducted to know the effect of growth and yield by different weed control duration using by 'chalok 1 ho', waxy maize, at Suweon in 1995. The emergence of weed and growth and yield of waxy maize on weedy check and 10, 20, 30, 40, 50, 60, 70, 80, and 90 days weed control and whole season weed control during cultivation summrized as follows; 1. Chenopodium album, Echinochoa crus-galli, Persicaria hydropiper and Panicum bisulcatum emerged as major weeds and dominant weed was Chenopodium album. 2. The number of emerged weeds grouped by mophologically ordered broad leaf weeds, grass weeds and sedge weeds. 3. 30 days weed control duration from the sowing effect to silking stage and 40 days weed control duration from the sowing decreased stem length, ear length, ear weight, number of plant, and number of ear. 4. The yield of weedy check, and 10 days weed control from the sowing showed no yield and 20, 30 and 40 days weed control from the sowing decreased to 76, 64 and 33 %, individually. 5. The yield loss of waxy maize on weeds can be prevent by 40 days weed control duration from the sowing.

• Weed & Turfgrass Science
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• v.3 no.2
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• pp.86-94
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• 2014

Survey was carried out in paddy fields to investigate the dominance of weed species and weed occurrence on 200 fields of southern Gyeonggi region in Korea during the year 2013. We observed 3 species of grass, 5 species of sedge, and 11 species of broadleaf and other weeds. The most dominant weed species was Eleocharis kuroguwai, followed by Echinochloa crus-galli, Sagittaria trifolia, Monochoria vaginalis, Scirpus juncoides and Bidens tripartita. The dominance value of E. kuroguwai and B. tripartita decreased compared to the survey results performed in 2005 but that of M. vaginalis, S. juncoides, S. trifolia and E. crus-galli increased. Weed occurrence increased from 2.83 g in 2005 to 3.51 g in 2013 based on weed dry weight per $m^2$. Occurrence ratio of annual weeds to perennial weeds changed from 45.2% : 54.8% in 2005 to 45.8% : 54.2% in 2013. If we analyze dominance of weed species based on the rice transplanting timing, E. kuroguwai and E. crus-galli were the most dominant weed species at mid-May transplanting, and M. vaginalis and S. juncoides were the most dominant weed species at late- May transplanting, and M. vaginalis and E. kuroguwai were the most dominant weed species at early-June transplanting. Since paddy weeds resistant to sulfonylurea herbicides are expected to be continuously increased, the regular monitoring of their occurrence and efficient control methods should be considered in future.

• Korean Journal of Weed Science
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• v.15 no.2
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• pp.105-114
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• 1995

Differences in critical period of weed competition were investigated among five types of rice(Oryza sativa L.) cultivation. Increase in weed-free period resulted in 1-2 days delay of heading date in machine transplanting and direct-seeding as compared with complete weed-free plot. When weedy period increased, there was no difference in heading date in transplanting cultivations. In direct-seeding, however, weedy period of 7-10 weeks after seeding(WAS) resulted in 4-7 days delay of heading date, whereas further increase in the weedy period caused rather 5-6 days advance in heading date. Weed-free period did not significantly affect yield components in conventional hand transplanting. In machine transplanting with 30-day-old seedling decreases in percent ripening and 1,000-grain weight were caused by weeds emerged within 4 weeks after transplanting(WAT). All yield components were decreased due to weedy period in machine transplanting with 10-day-old seedling. In direct-seeding weedy periods caused to decrease in number of panicles, number of spikelets, percent ripening, and 1,000-grain weight were 8-9, 4-5, 3-4, and 8-10 WAS, respectively. The critical periods of weed competition were determined as the following. In conventional hand transplanting weed-free must be maintained for either 4 weeks after transplanting or the rest period after 8 WAT. In machine transplanting with 30-day-old seedling weed-free must keep for either 5 weeks after transplanting or the rest period after 8 WAT. In machine transplanting with 10-day-old seedling weeds must be removed for either 5 weeks after transplanting or the rest period after 7 WAT. Weed-free must be kept between 5 and 7 WAS in flood direct-seeded rice and between 6 and 9 WAS in dry direct-seeded rice.

• Weed & Turfgrass Science
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• v.1 no.4
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• pp.24-30
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• 2012

This study was conducted to select the cover crops in organic apple orchard by estimating the coverage of each cover crops and time-periodic weed occurrence. Seeding of Festuca myuros and Trifolium repens showed high contents of soil organic matter and phosphorus as compared with control. Seeding of Trifolium sp., Hordeum vulgare and Secale cereal reduced relatively occurrence of weed in May and S. cereal among others showed the greatest effect in June. In July, seeding F. arundinaceae and Poa pratensis showed low coverage and a lot of weeds occurred in their field. Fifty one species were occurred as weeds and it needs to removal of high and broadleaf weeds such as Chenopodium ficifolium, C. album var. centrorubru and Humulus japonicus in spring to increase the rate of ground cover. P. pratensis having the lowest cover rate showed the similar dry weight of weeds as compared with control. Trifolium sp. and Persicaria hydropiper had a high correlation with contents of soil organic matter and C. album var. centrorubru had a correlation with contents of soil phosphorus by CCA analysis.

• Weed & Turfgrass Science
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• v.1 no.4
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• pp.13-17
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• 2012

A field experiment was conducted to investigate the effect of Acalypha australis occurrence on the growth and yield of soybean, to predict the reduction rate of soybean yield caused by competing with A. australis and to establish the economic threshold of A. australis for soybean cultivation. As the density of A. australis increase, the height and stem length of soybean were not affected by the competition with A. australis, however, the yield of soybean was decreased as 11~51% as compared with weed-free condition. The relationship between weed density and soybean yield was established as Y=415.5 / (1+0.003356X) and the reduction rate of soybean yield were predicted from this equation. Compared with the weed-free condition, the reduction rate of soybean yield were calculated as 0.3~9%, 17~29%, and 40~46% when the density of A. australis were 1~30, 60~120, and 200~250 plants $m^{-2}$, respectively. The economic threshold level of A. australis for soybean cultivation was established as 6.3 plants $m^{-2}$ from the Cousens' equation.

• Korean Journal of Weed Science
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• v.17 no.1
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• pp.1-9
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• 1997

The survey of weed community in paddy field was carried out to investigate the changes of weed species on 340 fields in Kyonggi Area in 1995, that is almost same condition as sampled in 1991. The weed species observed include 3 species of grasses, 5 species of sedges and 14 species of broadleaf and other weed. Herbicide treatment system in one time treatment vs more than two time treatment was 34:66 percentage. About 25 percentage among one time treatment system was used butachlor G. Ratio of annual weed vs perennial weed was 38:62, and then perennial weed ratio was high. Major dominant weed species were Sagitaria trifolia, Eleocharis kuroguwai, Echinochloa crus-galli, Bidens tripartita and Monochoria vaginalis. Weed occurrence was decreased as order of normal soil, poorly drained soil and saline soil. Dormant weed species were S. trifolia, E. kuroguwai, E. crus-galli and B. tripartita in normal soil and were S. trifolia, E. kuroguwai, E. crus-galli and Polygonium hydropiper in poorly drained soil, and were Scirpus planiculmis, S. trifolia and E. kuroguwai in saline soil. Weed occurrence was increased with delaying the transplanting time; dominant weed species were S. trifolia, E. kuroguwai, E. crus-galli and M. vaginalis in May transplanting field and were E. kuroguwai, S. trifolia, and C. serotinus in June transplanting field. Weed occurrence was decreased as order of non-plowing transplanting field, autumn plowing and spring plowing paddy field. Dominant weed species were S. trifolia, E. kuroguwai, E. crus-galli and M. vaginalis in autumn plowing, were S. trifolia, E. kuroguwai, E. crus-galli and B. tripartita in spring plowing, and were E. crus-galli, S. hotarui and S. trifolia in non-plowing transplanting field.

• Korean Journal of Weed Science
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• v.15 no.4
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• pp.254-261
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• 1995

The nationwide weed survey was conducted in lowland rice fields over whole country of Korea in 1992 in order to determine a change of weed community and to identify a major dominant weed species and/or problem weed. Based on morphological characteristics of weeds, population ratio of broad leaf weed was 42.6%, grasses weed-9.0%, sedges-33.4% and others were 15.0%. Annual weed was 33.4% while perennial weed was 66.6% in terms of life cycle of weeds. Meanwhile, there was different weed occurrence as affected by planting method of the rice plant. In hand transplanted paddy fields predominant weed species was Sagittaria trifolia L., Monochoria vaginalis Presl., and Aneilema japonica Kunth. In machine transplanted rice fields of infant and young rice seedling Eleocharis kuroguwai Ohwi. and S. trifolia L. were more predominant. There was high occurrence of M. vaginalis, Echinochloa crus-galli L., and Leesia japonica Makino in water seeding while E. crus-galli and Cyperus serotinus Rottb. were predominant weed species in dry seeded rice. Monoculture of the rice plant would cause to high occurrence of E. kuroguwai, S. trifolia, M. vaginalis, E. crus-galli, and Sagittaria pygmaea Miq and there was higher population of S. trifolia, S. pygmaea, M. vaginalis, E crus-galli, and E. kuroguwai in double cropping system based on rice culture. In particular, there was high different weed occurrence under different transplanting times. E. kuroguwai, S. trifolia, S. pygmaea, M. vaginalis, and C. serotinus were higher population at the transplanting of 25 May and S. trifolia, E crus-galli, C. serotinus, and M. vaginalis at 10 June and S. pygmaea, E. kuroguwai, M. vaginalis, S. trifolia, and E. crusgalli at 25 June in Korea, respectively. Autumn tillage in terms of tillage time would cause more predominant weed species such as S. trifolia, E. kuroguwai, M. vaginalis, and S. pygmaea while spring tillage was higher population of E. kuroguwai, S. trifolia, E. crusgalli, M. vaginalis, and S. pygmaea. In plain area of paddy field there was higher occurrence of E. kuroguwai, S. trifolia, M. vaginalis, E. crus-galli, and S. pygmaea and in mid-mountainous area S. trifolia, E. kuroguwai, M. vaginalis, E. crus-galli, and Ludwigia prostrate Roxb. while in mountainous area S. trifolia, M. vaginalis, Potamogeton distinctus Ben., E. kuroguwai, and E. crus-galli were. In 1992 the most ten predominant weed species at the rice field of Korea based on summed dominant ratio(SDR) were E. kuroguwai > S. trifolia > E. crus-galli > M. vaginalis > S. pygmaea > C. serotinus > L. prostrate > P. distinctus > A. japonica > Scirpus juncoides Roxb.

• Korean Journal of Weed Science
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• v.8 no.2
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• pp.141-155
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• 1988

We have large areas of forests in our country where various types of trees can grow. Since Japan geographically locates on a wide region with the extention of 3,000 km south and north, the climate varies from subtropical to subarctical one. Many mountains additionally make the climatic condition more complicated. Thus, we are able to see many kinds of trees in our forest areas. We have also frequent rainfalls through whole season and the precipitation reaches approximately 1,500 mm per year in many forests areas. In some rainy regions, it sometimes account for more than 2,000 mm. The condition is so advantageous for the growth of weeds and shrubs that it makes them very strong competitors with plantation trees in our forestries. It, therefore, may be said that the most important problem in Japanese forestries is to combat with undesirable vegetations continuously and to keep trees from weeds.