Effect of herbicide and application of superphosphate and subterranean clover seed on regeneration of vulpia in pastures

Abstract

Summary. The annual grass vulpia has become one of the main weed problems in permanent pasture and cropping areas across southern Australia. The effect of herbicides and management (application of superphosphate and subterranean clover seed) on regeneration of vulpia in pasture was evaluated over a 2 year period at 6 sites in central and southern New South Wales (Beckom, Wagga Wagga, Eugowra, Bathurst, Holbrook and Millthorpe) during 1989–91. Four herbicide strategies (nil, spraytopping with paraquat in spring 1989, winter cleaning with simazine in winter 1990, and spraytopping with paraquat in spring 1989 followed by winter cleaning with simazine in 1990) were evaluated at a low (no added superphosphate or subterranean clover seed) and high level (250 kg/ha additional superphosphate applied in autumn 1989 and again in autumn 1990, plus 10 kg/ha subterranean clover seed broadcast in 1989) of management.

Herbicides decreased the incidence of vulpia (as assessed from seedling density and pasture composition measurements) at low and high levels of management, with simazine and the combined paraquat plus simazine treatment providing more effective control than paraquat. The population of vulpia, however, increased rapidly on both the simazine and paraquat treatments with time. On the paraquat plots, this resulted in a similar or greater vulpia density as the unsprayed control within 2 years of application. The higher level of management encouraged greater density of subterranean clover and nitrophilous species (e.g. barley grass where present), resulting in greater competition against vulpia, and extending the period of control conferred initially by the herbicides. Control of vulpia over the longer term will require integration of herbicides with other management strategies (e.g. superphosphate, additional seed, careful grazing management). Such an approach needs to be implemented on a more regular basis than is currently practised if the impact of vulpia in pastures is to be minimised.