Biological and ecological impact of serrated tussock (Nassella trichotoma (Nees) Arech.) on pastures in Australia
M.H. Campbell, NSW Agriculture, Orange Agricultural Institute, Orange, New South Wales, 2800, Australia.
Because serrated tussock is unpalatable and difficult to digest it can reduce carrying capacity by up to 97%. Animals graze associated plants with increasing severity as ground cover of the weed increases. In heavy infestations almost all native and introduced pasture species are eliminated. If control is attempted early in the invasion process it can be successful and profitable. If attempted after a substantial proportion of the property is infested heavy financial outlays are necessary and control is difficult to achieve on non-arable land with low rainfall and infertile soil.
Serrated tussock has many ecological and biological features that explain its success as a weed. The ability to produce enormous numbers of seeds that are widely distributed by wind and establish readily facilitates invasion of land unprotected by vigorous pastures. Despite relatively slow seedling growth it invades because animals graze more palatable plants. Once established individual tussocks live for long periods and withstand grazing, drought, burning, infertile soils, unfavourable aspects and competition.
Control on arable land depends on replacing the weed with a leniently grazed phalaris dominant pasture protected from reinfestation by removing invading tussocks. Where pasture improvement, fertilizer application and herbicide treatment are not undertaken, due to environmental or economic factors, the weed dominates.
Control on non-arable land under the present economic conditions is achieved by aerial application of flupropanate which, without sowing pastures, is only a short term solution and kills susceptible native grasses. Seedhead production can be stopped by applying 0.22-0.45 kg a.i. ha-1 glyphosate 2-8 weeks before the seedheads begin to emerge. Removal of seedlings with low rates of flupropanate offers a low-cost method of control. It requires the removal of mature tussocks initially, treatment of seedlings each time there is a major invasion and establishment of pasture species that are tolerant to the low rates. Control in native grass pastures is difficult due to their inability to compete with the weed when grazed and the susceptibility of Danthonia spp. and Microlaena stipoides to flupropanate. Control in areas where pastures are ineffective or unprofitable is being attempted by afforestation.
Plant Protection Quarterly (1998) 13 (2) 80-86.