Effect of stubble cover on the efficacy of some soil-incorporated herbicides

Abstract

Three field experiments were conducted near Kingaroy in south-eastern Queensland to determine the effect of sorghum stubble on the efficacy of the pre-plant, soil-incorporated herbicides pendimethalin, trifluralin and vernolate. Herbicides were applied to three stubble ranges (1 1 to 36% cover) in experiment 1, to stubble levels of 10, 20, 30, 40, and 50% cover in experiment 2, and approximately 0, 25 and 50% in experiment 3. In experiment 3 the effectiveness of incorporation with stubble mulch machinery consisting of chisel plough with attached rod weeder was compared with that achieved by conventional incorporation methods of coronet tines with mounted harrows and offset discs followed by tines and harrows. Treatment effects were examined by analysis of variance and by linear correlations between stubble cover and herbicide efficacy. Good to excellent weed control was achieved by all herbicides at stubble levels up to 50% cover with incorporation by stubble mulch machinery. Trifluralin efficacy was aided by stubble cover in one experiment. Incorporation by stubble mulch machinery was at least as effective as conventional methods.