SHORT-TERM SPLIT APPLICATION EFFECTS OF GRASS-SPECIFIC HERBICIDES ON QUACKGRASS (ELYTRIGIA REPENS) UNDER FIELD CONDITIONS

Field experiments were conducted at the Lacombe Research Station from 1989 to 1991 to determine if short-term, split applications of grass-s pecific herbicides would improve quackgrass control relative to single applications. Quackgrass infested plots were planted to canola the fi rst year and barley the following year. Glyphosate applied at 880 g/ha controlled quackgrass to a greater extent and for a longer time perio d than any of the grass-specific herbicides. In contrast to glyphosate , none of the grass-specific herbicides controlled quackgrass 1 yr aft er treatment. Quackgrass control with sethoxydim or fluazifop-P was us ually similar when applied as single or short-term, split applications . In contrast, quizalofop often provided better quackgrass control and higher crop yields when short-term, split applications were compared to a single application with the same total amount of quizalofop. Howe ver, the extent of increased quackgrass control is difficult to justif y due to increased application costs and inconvenience.