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.
Pasture production, pasture composition and quality, and liveweight, body condition and wool growth of Merino weaner wethers were monitored over 2 seasons and at 2 stocking rates (4 and 8 sheep/ha) on a mixed annual grass-legume pasture sprayed with propyzamide to control grasses. Propyzamide virtually eliminated annual grasses from the pasture (less than 5 kg/ha of grass dry matter in spring v. 403 kg/ha on untreated pasture in 1981) and this carried over into the second season (61 kg/ha v. 647 kg/ha in spring 1982). Propyzamide treated pastures had less total dry matter (P = 0.05) throughout 1981: however, except for a single sample date, there was no effect of propyzamide on total available pasture in the second season. Increased growth of clover and capeweed compensated for the absence of the grasses. The higher stocking rate reduced available clover, capeweed and total dry matter (P = 0.05) throughout both years. Sheep grazing grass-free pastures had lower liveweights during winter in both years, but made compensatory gains during late spring and summer consistent with the higher quality (1.6 v. 1.07% nitrogen when sampled in January) of propyzamide treated pastures. In 198 1, wool growth rates were reduced at the higher stocking rate and total clean wool production was reduced from 4.55 kg/sheep at 4/ha to 3.65 kg/sheep at 8/ha. Pasture treatment had no effect on wool production in either year. The implications of using selective herbicides to remove the annual grass component of legume-based annual pastures in south-western Australia are dis cussed in relation to pasture and sheep production.
The improvement of pastures by the use of a range of h~rbicides to eliminate grasses, and their effect on populations of the take-all fungus (Gaeumannomyces graminis var tritici = Ggt) were studied in the field (at Esperance Downs, on the south-coast of Western Australia) from 1982 to 1985. Field trials were conducted to evaluate three herbicide treatments (2,4-D amine + propyzamide; 2,4-D amine + paraquat; paraquat/ diquat) and an unsprayed control. A pot trial involving these treatments with two levels of nitrogen was undertaken to confirm treatment effects observed in the field trial.All herbicide treatments resulted in reduced grass composition of pastures, in both the year of spraying and in the second year of pasture, but reduced dry matter production in the year of spraying. In the year of spraying, however, inoculum of Ggt was reduced (P < 0.1) only following the 2,4-D amine + propyzamide treatment and was greater (P < 0.1) after 2,4-D amine + paraquat treatment than the unsprayed treatment. Despite reduced grass levels in the herbicide-treated plots in the second year of pasture, Ggt inoculum did not differ between treatments, nor did it after a wheat crop which followed a second year pasture.There was high correlation (P < 0.001) between disease levels and dry weights of grasses in the pot trial. There was significantly less (P < 0.001) grass in pots treated with herbicides compared to the unsprayed control but no difference (P > 0.05) was evident between treatments. Inoculum levels were lower (P < 0.05) in the treated pots than the unsprayed control with no evidence of differences among treatments (P > 0.05). Nitrogen level had no effect on disease (P > 0.05).All herbicide treatments tested reduced grass level and total dry matter, both in the field and in pots.Whereas in the pot trial reduced grass levels resulted in reduced Ggt inoculum, in the field such a reduction occurred only with the 2,4-D amine + propyzamide treatment and only in the year of spraying. Herbicide treatments had no effect on Ggt inoculum in second year of pasture or crop. Unknown soil and environmental factors in the field precluded a simple relationship between grass level in pasture and subsequent level of Ggt inoculum, and where such a relationship did occur (2,4-D amine + propyzamide treatment) it appeared to be shortlived.
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