Effect of time and rate of application of herbicides on serrated tussock (Nassella trichotoma) and improved pasture species. 1. Glyphosate and 2,2-DPA

Abstract

The effect of three rates of glyphosate (1, 3 and 5 kg a.i. ha-1) and two of 2,2-DPA (21 and 33 kg a.i. ha-1), each applied in October 1972, January 1973, April 1973 and July 1973, on serrated tussock and associated improved species (Phalaris aquatics, Trifolium repens, T. subterraneum) was ascertained in an experiment near Bathurst, New South Wales. The effect of the herbicide treatments on the improved species was measured in October 1973 and the percentage kill of serrated tussock recorded in May 1974. Increasing the rate of glyphosate increased the percentage kill of serrated tussock (up to a mean of 77% with 5 kg a.i. ha-1) ; time of application had no significant effect on percentage kill. No glyphosate treatment resulted in a commercially acceptable kill of serrated tussock (above 90%). Thus the herbicide was inferior to 2,2-DPA which produced a 95% kill when applied in summer. P. tuberosa was more tolerant of glyphosate and 2,2-DPA than serrated tussock and recovered from all treatments. T. repens and T. subterraneum recovered from glyphosate and 2,2-DPA applied in summer. Thus it proved possible to selectively remove a large proportion of a serrated tussock infestation with 2,2-DPA or glyphosate, applied in summer, without permanent damage to the associated improved species.