|Botanical Name||Nassella trichotoma|
IdentificationA perennial, drought-resistant, tussock grass, it has dense, fibrous roots which grow to 1 metre in depth. The green to yellowish-green tussocks have a basal diameter up to 150mm, a height of up to 700mm and a leaf spread of 700mm. Leaf bases are tight, swollen (shallot-like) and whitish, compared to many other Stipa species which have purplish leaf bases. Leaves are thin (1mm), hard, fairly stiff, tightly rolled and feel rough when drawn downwardly between the fingers. The leaf blades are bright green in seedlings, with whitish tips in winter, but turn dull green and droop at maturity. The short (1 to 2mm), white, hairless ligule and lack of auricles, is the best identification guide because other similar tussocks either have hairs at the ligule or have no ligule at all. During flowering, nassella assumes a purple tinge owing to the purple spikelets. These numerous flowerheads are in the form of open branched panicles which grow from 250 to 950mm long and are erect when young but weep over the tussock when mature.
HabitatsIt is found mainly on light textured soils of low fertility which are subject to regular moisture deficiencies, but it also occurs on fertile river flats.
Impact to Biota and EcosystemsNassella tussock is an extremely vigorous, invasive plant which crowds out desirable pasture species, reducing stock carrying capacity up to 90%. Nassella forms indigestible balls in the stomachs of stock and if forced to graze it they may lose weight and die, as the plant has a high fibre content and a low nutritive value.
Dispersal Routes, Vectors, Infestation SourcesThe only method of spread is by seed. The seed head breaks off near the base of the plant and may become airborne, spreading up to 16kms away from the mother plant. The seeds, aided by the roughened seed coat and the tuft of hairs at the base, also cling to wool, bags, clothing etc. Seeds are also spread on machinery, in hay, water, mud and the droppings of animals. Each plant produces up to 120,000 seeds annually. The individual seeds are small, oval (2mm long x 1mm wide), light brown to fawn, with a basal ring of hairs and a seed hair 25mm long. Nassella normally flowers and seeds between October and December.
The most commonly used and effective control method is grubbing, which is adequate provided the base of the tussock is removed completely and this is carried out before plants are flowering and/or seeding. Herbicides such as Dalapon or Glyphosate are also used but are not nearly as effective as grubbing.
Glyphosate is used in some situations but is ineffective on large plants. Physical control is the most effective control method.
It is important that land management practices enable ready detection and eradication. Every effort should be made to prevent plants seeding, especially on new sites, and to prevent the spread of seed by the movement of livestock, produce, machinery and soil.
Nassella tussock is an Eradication Pest Plant in the Bay of Plenty Region. All sightings of this plant should be reported to a Pest Plant Officer who will organise for its control.
Nassella tussock probably arrived in NZ from its native South America late last century. Active and intensive control programmes have markedly reduced its density to the extent that it no longer causes any major reduction in agricultural production, however it is still recorded on many sites throughout NZ where intensive control work continues to ensure infestations do not increase in size.
This plant is prohibited from propagation, sale and distribution within the Bay of Plenty!