The effect of the isopropylamine salt of glyphosate and the ethyl ester of quizalofop on the rhizome bud viability of five quackgrass biotypes was tested. Two bioassays used were: direct measure of the growth of the bud on an agar medium and determination of the respiratory activity with tetrazolium chloride. The response to herbicide treatments differed among biotypes. The growth bioassay showed lower viability than the tetrazolium bioassay. Quizalofop reduced viability more than glyphosate. Viability of untreated buds increased with increasing distance from the base of the rhizome. The viability of herbicide-treated buds was more or less equal regardless of the position. It appeared that both herbicides were translocated to all the rhizome buds.
