Control of grader grass (Themeda quadrivalvis)

Abstract

Increased degrees of stubble shading after cutting did not significantly reduce the density of grader grass; mature seed was produced even under 75% shade. Reduced density following cutting at full flowering is considered to be a direct function of plant age-the older the population the more susceptible it is to defoliation (by Gramoxone [paraquat 20%] at 1.5 fluid oz + wetter 0.5 %/ 3.5 gal water, applied to wetting). Burning and severe defoliation encouraged germination of grader grass seed whereas allowing the grass to remain undisturbed suppressed germination. Management systems which denude the soil encourage and increased soil cover reduces grader grass. Reduction is permanent because seed degenerates in the soil. In lower rainfall areas with sparser vegetation it may be difficult to maintain adequate cover to suppress grader grass. Early wet-season grazing of native pasture improved with Townsville stylo (Stylosanthes humulis) was shown to give the highest cattle productivity but also encourages invasion by grader grass. Excessive burning would pre-dispose native grassland to invasion, while moderate grazing of improved pastures in the wet tropics would preclude regeneration of grader grass.