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Vulpia is a widespread weed of temperate Australian pastures, and readily replaces more productive species. Short-term management of vulpia is possible with herbicides but densities rapidly increase in poorly competitive pastures after herbicide application. A field experiment at Wagga Wagga, NSW, examined the effect of 2 fertility levels and 4 pasture types [subterranean clover sown at 1, 25, 100 kg/ha, and subterranean clover (25 kg/ha) + annual ryegrass (20 kg/ha)] on 2 densities of vulpia (50,5 500 plants/m2) from 1990 to 1994. Initially vulpia plant density was inversely related to sowing rate of subterranean clover, but over time this effect declined as the subterranean clover populations converged. Presence of annual ryegrass always resulted in lower vulpia plant, panicle and seed densities compared with treatments where subterranean clover only was present. Respective densities per m2 in 1993 for the average of the subterranean clover monocultures and for annual ryegrass plus subterranean clover were: plant 1315 v. 265; panicle 6700 v. 130; seed 542 400 v. 3460. The effect of drought in 1994 and presence of annual ryegrass were shown to significantly lower the sustainable population of vulpia at Wagga Wagga from 5000–6000 to