Control of annual grasses by spraytopping and the effect on triticale grain yield

Abstract

IA range of pre-season management treatments was imposed on a mixed annual grass sward in October 1987, prior to planting triticale into a cultivated and a direct-drilled seedbed in June 1988. The management treatments included three rates of glyphosate: Roundup« (110, 180, 360 g a.i./ha); two rates of paraquat: Gramoxone« (100, 200 g a.i. ha); and one rate of fluazifop-butyl: Fusilade« (53 g a.i./ha ¦ Pulse« wetting agent). All treatments decreased potential grass regeneration, with V. bromozdes being the least affected. Improved control was achieved by increasing application rate, and by adding a wetting agent to fluazifop. Actual grass seedlings emerging within the crop followed a similar pattern to potential grass regeneration. Grass emergence, particularly of V. bromoides and L. rigidum, was always greater on the direct-drilled seedbed. Grain yield was greater on the prepared seedbed. On both seedbeds, yield was inversely related to grass DM 97 days after sowing (DAS) and grass weed seedling numbers 50 DAS. The effectiveness of the herbicides appeared to be related to maturity dates of the target species. The high potential seed-set of the annual grasses present (> 500 000/m2), of which V. bromozdes was the main component, highlights the difficulty of controlling such species. It is suggested that the large apparent decline from total seed-set to potential seedling numbers (14000/m2) resulted from the high stocking pressure by sheep over summer. For a number of annual grasses, a more rapid method for determining seed number based on seed weight and seedhead number is proposed, providing a more informed basis for decision making. We conclude that spraytopping to maximize yield of later sown direct-drilled crops (e.g. triticale) is essential, despite the difficulty in optimizing timing of spraytopping in mixed pasture swards.