The effect of application of selective herbicide, MDBA, togather with over-sowing grass which could form the dense canopy on the control of Rumex obtusifolius were investigated in a permanent meadow at Kuju Agricultural Research Center, Kyushu University during 1990-92. The treatments at the rates of 75,100 and 200ml
100l water of spraying MDBA once (late autumn) a year and at the rates of 100 and 200 ml
100l twice (late autumn and after the 1st harvest) a year were employed. Dactylis glomerata was over-sown at the start of investigation in 1990. The results obtained were as follows: 1) Though the application of MDBA at all rates of sparaying once a year reduced the number of Rumex obtusifolius to a large extent, the plants were not entirely removed from the meadow. 2) Under the application of MDBA at all rates of spraying twice a year, Rumex obtusifolius in smaller size almost disappeared and the plants in larger size which grew a retard were gradually decreased in population by the canopy shade of Dactylis glomerata. By the end of the investigation in the 2nd year Rumex obtusifolius were entirely removed 3) A large number of seedlings of Rumex obtusifolius were found in a bare lands of the meadow, but not in areas densely canopied with Dactylis glomerata.
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