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Establishment of surface-sown perennial pastures to replace annual grass weeds

M.H. Campbell

Agricultural Research and Veterinary Centre, Orange, NSW 2800

Nitrophilous weeds (broadleaved plants and annual grasses) can be replaced by perennial grass dominant pastures. On hill country, aerial techniques have to be used to establish the improved species. These techniques have been successful in replacing most nitrophilous weed associations but they can fail when Lolium rigidum is the major annual grass component. Thus experiments were undertaken (-1985-89) at Boorowa, N.S.W. to investigate methods of replacing L. rigidum with perennial grass pastures.


Improved species (Medicago sativa, Phalaris aquatica, Dactylis glomerata) were surface-sown after herbicide treatments. Seeds were treated with permethrin to reduce losses from ants and a P + S fertilizer applied. In experiment 1 the effect of 2 and 3 treatments with glyphosate in the control of sequential germinations of L. rigidum was examined. Each treatment had glyphosate applied 62 and 8 days before sowing; the third spraying was 14 days after sowing when L. rigidum and M. sativa had germinated but D. glomerata and P. aquatica had not. In experiment 2, 10 treatments were spray-topped the spring before sowing and 10 were not. In experiment 3, 11 treatments were heavily grazed with sheep for 7 days in October after improved species had established and 11 treatments were not grazed. Plant numbers in experiments 1, 2 and 3 and ground cover of weeds in experiments 1 and 3 were measured in September or October; ground cover of weeds in experiment 2 was measured in May.

Results and discussion

Increasing the number of sprayings from 2 to 3 and spray topping increased the number of sown grass plants present in their first spring while grazing reduced the numbers (Table 1). M. sativa numbers were not affected by spray topping or grazing but were reduced by the third spraying because seeds germinated faster than the grasses. Despite the increase in plant numbers and decrease in ground cover of weeds caused by treatments in September and October, by late November L. rigidum had recovered in all experiments and completely dominated the sown species. Thus future investigations need to examine, inter alia: two years of spray-topping before sowing; spraying L. rigidum when it overtops sown species; and extended grazing with cattle.

Table 1. Effect of various treatments in the first spring after sowing

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