The Use of Grasses as a Weed Management Technique in a Degraded Riparian Site

SYNOPSIS

A stand of Eucalyptus grandis growing in the riparian zone of the Sabie River in the eastern Transvaal was clearfelled during 1992, leaving the site disturbed, covered with slash and infested with alien invader plants. A randomised complete block trial was conducted on this degraded site to evaluate the ability of three combinations of six perennial pioneer and climax grass species to suppress weed infestation. To facilitate the grass establishment, the site was burned during December 1992 and the grasses were seeded two days after the burn.

Because of the site's gentle slope (0–5°), no visible soil erosion occurred after the fire. The alluvial soil and the ash from the burn provided an ideal seedbed for the seeded grasses. With these favourable site conditions, combined with relatively good rains, a significantly higher vegetation cover was obtained within three months in the seeded plots (mean = 93 %) as opposed to the control plots where no grass was seeded (mean = 84 %). Plots that included the seeded Panicum maximum, Setaria sphacelata var. sericea and Chloris gayana, as well as the naturally occurring grasses and sedges (e.g. Setaria megaphylla), had a significant suppressive effect on the alien invader plants (e.g. Solanum mauritianum).

Although regeneration of alien invader plants are suppressed by the grass cover to a significant extent, it will not eliminate the need for follow-up chemical or manual control of alien invader plants. The use of grasses as a weed management technique in burnt riparian sites could be part of an integrated weed management strategy where multiple tactics are used to manage alien invader plants.