Establishment and development of surface sown pasture species in a nitrophilous weed association: effect of herbicide rate

Abstract

In an experiment carried out between 1976 and 1979 near Orange, New South Wales, the effects of four rates of glyphosate (0.1 25, 0.25, 0.5 and 1.0 kg/ha active ingredient (a.i.)) and three rates of amitrole (0.5, 0.75, 1.0 kg/ha a.i. in association with 2.5 kg/ha a.i. 2,2-DPA) on the suppression of a nitrophilous weed association (broadleafed plants, annual grasses, native perennial grasses, annual legumes) and the resultant establishment and development of surface sown pastures species (Medicago sativa, Phalaris aquatica, Dactylis glomerata, Festuca arundinacea) were measured. The length of weed suppression in the year of spraying (1976) was the most important factor in the eventual development of the sown species. Glyphosate at 1.0 kg/ha a.i. gave better weed suppression for longer (up to and beyond 23 weeks after spraying) than any other herbicide treatment and allowed sown species to establish and survive the first summer better and thus produce a better pasture three years later. Weed suppression between 8 and 19 weeks after spraying affected the initial establishment of sown species; in general, establishment was better on herbicide treatments that reduced ground cover of the weed association to less than 30% in this period. Rate of weed suppression had no effect because no sown species germinated in the eight weeks after spraying. Three years after treatment the ground cover of the nitrophilous weed association was 31% on the best herbicide treatment (glyphosate, 1.0 kg/ha a.i.) and 83% on the unsprayed control; the respective ground cover of sown species was 60% and 7%. The increase in ground cover of sown species during the three years was on most treatments almost entirely due to the increase in basal area of P. aquatica.