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The effect of grass-selective and broad-spectrum herbicides in pasture:wheat rotation experiments were studied from 1981 to 1986 at Esperance, W.A. The quantity of pasture and the proportion of grass present in the pasture phases were determined. Pastures were grazed by sheep. Incidence and severity of take-all and grain yield were measured in the wheat phases. The rotations studied were either a 2 year pasture: 1 year crop or 1 year pasture: 1 year crop. Herbicide treatments greatly decreased the grass content of pastures in the year of application, and this effect carried over to the second year in the 2 year pasture: 1 year crop rotation. Herbicide reduced total pasture yield in the year of application, but not in the year following. Herbicide treatment of pastures decreased the incidence and severity of take-all in the following wheat crop. Crop yields were increased following treated pastures and to a greater extent than could be exdained bv decreased take-all alone. Incidence of take-all depended primarily upon the quantity of grass in the previous pasture (5.4% incidence of take-all per 100 kg ha-1 grass dry matter in the previous pasture). Incidence of take-all was also related to the incidence of take-all in previous wheat crops and the quantity of grass in the pasture in the preceding two years. |
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