Use of herbicides for selective removal of Eragrostis curvula (Schrad.) Nees from a Pennisetum clandestinum pasture

Abstract

In 3 experiments near Candelo, New South Wales, the effectiveness of tetrapion, glyphosate and 2,2-DPA in selectively removing Eragrostis curvula (agronomic type Tall Chloromelas) from a Pennisetum clandestinurn pasture was determined by applying each at various rates in each season of the year in 1981-82 (experiments 1 and 2) and in 1983 (experiment 3). Experiment 4 examined the effect of the herbicides on 3 cultivars of P. clandestinum when applied in each season in 1983-84. Tetrapion (2.25 and 3.00 kg/ha a.i.) was the most effective herbicide in killing E. curvula and promoting P. clandestinum in experiments 1 and 2, but, in experiment 3, glyphosate and 2,2-DPA were equally effective in killing E, curvula at 3 (glyphosate) and 2 (2,2-DPA) of the 4 application times. The differences between the results of the experiments were attributed to the herbicide being leached faster by the higher rainfall and being immobilised by the greater amounts of dead foliage of E. curvula in experiment 3. Despite occasional success in killing E. curvula, glyphosate and 2,2-DPA could not be considered for selective use as both were much more phytotoxic to P. clandestinum than tetrapion (experiment 4). Time of application had little influence on the selectivity of tetrapion, the least effective being May-June. In experiments 1 and 2, E. curvula was still well controlled by P. clandestinurn 5 years after the application of tetrapion. Pennisetum clandestinum cv. Crofts was more tolerant of tetrapion than were cvv. Whittet or Common.