• Korean Journal of Weed Science
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• v.16 no.3
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• pp.194-199
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• 1996

Seed size and days required to reach specific growth stages were determined for Echinochloa crus-galli (L.) P. Beauv. varieties which are major grass species found in Korean paddy field and the results were compared with E. frumentacea (Roxb.) Link. In addition, responses of the Echinochloa species on preemergence herbicides (molinate, esprocarb, and mefenacet) were investigated with respect to time of application. One thousand seed weight of E. crus-galli var. oryzicola was about 3 times heavier than that of var. praticola, but was not significantly different that of E. frumentacea. Days requited to reach the 2.5 leaf-stage (LS) were 11, 13, and 14 days after seeding for E. frumentacea, E. crus-galli var. oryzicola, and E. crus-galli var. praticola, respectively. E. crus-galli var. praticola was more sensitive to molinate, esprocarb and mefenacet than var. oryzicola and the sensitivity of both the varieties decreased as the time of application LS was delayed. However, there was no great difference in the response for E. frumentacea when applied between 1.5 and 3.0 LS. In thiocarbamate hebicides esprocarb was more active to Echinochloa species than molinate and the higher the active ingredient of the herbicides, the greater was the activity to Echinochloa species. Differential susceptibility of Echinochloa species to the herbicides was not related to the seed size, but to the early growth stages at the time of herbicide application which were affected by the seed size.

• Korean Journal of Weed Science
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• v.4 no.1
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• pp.96-106
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• 1984

Changes in weed floras and development of plant resistance to herbicides seemed to be closely related with increased and repeated use of herbicides. Herbicide use increased from 5% of the total consumption of pesticide in 1950 to 45% in 1976 in world basis. About 200 herbicides have been introduced to agriculture so as to control about 206 weed species which have been recorded important to human beings. In Korea, there was about 351 times in increased use of herbicides from 1966 to 1982. Interspecific selection by herbicide is mainly responsible for changes in weed floras and resulted in varying tolerance or susceptibility to herbicides, together with the changes of agricultural practices. The present trend toward continuous cereal cultivation throughout world will lead to type of changes in weed floras favorable to therophyte which can survive under unfavorable conditions as seeds rather than the types of geophyte which can survive unfavorable seasons as buds placed below soil surface. However, geophyte such as Sagitaria pygmaea, and Scirpus jurtcoides, and Cyperus rotundus and Cynodon dactylon in temperate warm climate become severe paddy weeds, presumably because of the removal of annual weeds by herbicides. Since differential tolerance to 2,4-D was firstly reported in Agrostis stolofera, about 30 species of weeds in 18 genera are presently known to have developed resistance to triazine herbicides. Resistance of weed biotypes to triazine herbicide is not mainly due to limited absorption and translocation or to the difference in metabolism, but is the result of biochemical changes at the site of metabolic activity, such as a loss of herbicide affinity for triazine binding site in the photosystem II complex of the chloroplast membrane. Genetical study showed that plastid resistance to triazine was wholly inherited through cytoplasmic DNA in the case of Brassica campestris. Plant tissue culture method can be utilized as an alternate mean of herbicide screening and development of resistance variants to herbicides as suggested by Chaleff and Parsons. In this purpose, one should be certain that the primary target process is operational in cell culture. Further, there are a variety of obstacles in doing this type of research, particularly development of resistance source and it's regeneration because cultured cells and whole plants represent different developmental state.

• Korean Journal of Weed Science
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• v.10 no.4
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• pp.338-343
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• 1990

The intraspecific susceptibility of twelve Echinochloa colona(L.) Link ecotypes to herbicides was studied at three different stages of growth. At germination and post-germination stage, the Batangas ecotype was most susceptible to both butachlor (N-butoxymethyl-2-chloro-2', 6'-diethylacetanilide) and thiobencarb (S-4-dichlorobenzyldiethylthiocarbamate), whereas the Bukidnon ecotype was the most tolerant. The susceptibility of the ecotypes used was not associated with the seed weight and maturity. When the preemergence herbicides were applied at the 2-leaf stage of the ecotypes, the Nueva Ecija ecotype was least susceptible to butachlor at 1 ppm, but it was most susceptible to thiobencarb. The reverse was exhibited by the Cagayan ecotype. Differential susceptibility of the ecotypes to propanil (3', 4'-dichloropropionanilide) as determined by the necrotic length of the third leaf of 20-day-old seedlings was pronounced in the Camarines Sur, Iloilo, and IRRI (red) ecotypes. However, no necrotic tip appeared in the Cagayan and Batangas ecotypes. The differential responses varied with the type and the concentration of the herbicide studied and the growth stage of the ecotypes.