Tropical Grasslands (1997) Volume 31, 24–30

The influence of grazing management on weed invasion of Lolium perenne pastures under subtropical conditions in South Africa

F.R. McKENZIE

Department of Grassland Science, University of Natal, Scottsville, Republic of South Africa

Abstract

Lolium perenne (perennial ryegrass) exhibits poor persistence in subtropical environments and this is often characterised by weed invasion. Grazing management may enhance the potential of perennial ryegrass to successfully outcompete weeds. Perennial ryegrass pastures were subjected to various grazing frequencies and intensities and the level of weed invasion monitored over 2 years. The proportional contribution of weed species tillers to total sward tillers was higher during late summer and autumn (4–20%), than winter (2–10%) or spring (1–4%). Pastures infrequently grazed incurred lower levels of weed invasion (56–256 weed tillers/m2 in Year 1, and 105–623 tillers/m2 in Year 2) than those frequently grazed (105–625 tillers/m2 in Year 1, and 256–2489 tillers/m2 in Year 2). Grazing intensity, however, did not influence the level of weed invasion. It is concluded that the invasion of perennial ryegrass pastures by weed species, particularly during the summer, can be minimised by sufficiently long grazing intervals (> 21 days).

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