Serrated Tussock (Nassella trichotoma)

Family: Poaceae

Growth Habit: Young plants are erect and densely tufted with tightly inrolled leaves. As the plant grows to maturity, the later leaves become longer, the tips turning to brownish green or, in winter, a bleached straw colour. Leaves at all growth stages feel rough or serrated if the finger and thumb are drawn down the blade. Grows to 50 cm in height, with a deep root system and can occupy 75 sq cm.

Very similar to native Tasmanian Poa grasses. According to DPIPW the following characteristics help distinguish Serrated Tussocks:

  1. Leaf bases of serrated tussock are more tightly packed and more slender than those of other tussocks and are never purple or blue-green, but a whitish colour (see illustration below).
  2. In summer when most other grasses have dried off to a straw-colour, the young serrated tussock plants still retain their bright green colour, except for the tips which are bleached.
  3. At the junction of leaf sheath and blade most grasses carry a small flap known as a ‘ligule’. In the case of serrated tussock this is white, papery, rounded at the tip and never hairy (see illustration).
  4. The upward-pointing barbs on the leaf blade, which gives them their rough or serrated texture, are minute and almost invisible to the naked eye. If the leaves appear at all hairy, the plant is not serrated tussock (see illustration).
  5. The seed head breaks off whole. The previous year’s seed heads do not generally remain on the plant.
  6. Flowering and seeding heads are a dark purple due to the colour of the two ‘glumes’ surrounding the seed (see illustration).
  7. Seed of serrated tussock is unlike the seed of any of the other tussock grasses with which it is likely to be confused (see illustration).
  8. For help in identifying serrated tussock, search the Dennis Morris Weeds and Endemic Flora Database for serrated tussock illustrations.
  • If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.

Type of Plant: Perennial, tussock forming grass.

Flowers: Flower stalks usually appear in spring (although they can appear earlier or later, depending on the availability of water). The flowering heads are carried on slender stalks slightly longer than the leaves. Each flower head is an open, branched panicle, the primary branches in pairs, slender and drooping. A tussock in full flower in early summer presents a distinctly purple appearance due to the large number of purple florets.

Serrated Tussock Seeds

Fruit/Seed: Each floret produces one seed, about 2 mm long, pale straw coloured, with a tuft of short hairs at the base and a long, slender, twisted awn from the tip.

Dispersal: When the seeds are ripe the flower stalk becomes very brittle, strong wind breaks it off and the whole seed head is blown along until it lodges against some obstacle. As the seed head dries out, the seeds are released and fall to the ground to begin a new colony.

In Tasmania human activities have been responsible for introducing and spreading the weed. The tuft of basal hair and the awn of the seed allows it to catch on the fleece of sheep. It may also be picked up in mud, on the hooves of livestock, on cultivating implements, in vehicle tyres or on firewood. Quarantine measures now in force are aimed at preventing its spread by any of the above means.

Distribution: Most infestations of Serrated Tussocks occur in the southeast, the Tasmanian Midlands, east coast, and in localised populations in the south of King Island. In the Tamar, there is an infestation in Mt Direction. Contact Biosecurity Tasmania on 03 6165 3777 if you identify any Serrated Tussocks.

Status: Serrated tussock is declared a Noxious weed under the Noxious Weeds Act 1964 in Tasmania and is therefore subject to eradication, with all affected land placed under quarantine.

Weed Impact:

  • Significant weed of grazing land.
  • Dense infestations may completely swamp out all other pasture components, rendering large areas incapable of supporting livestock.
  • Serrated tussock is of very low nutritional value to stock and if grazed, the leaves can form indigestible balls that can result in loss of condition and possible death.
  • Serrated tussock threatens the biodiversity values of Tasmania’s native grasslands, displacing native species and often going undetected until infestations reach a large size. Serrated tussock will also invade other vegetation types such as grassy woodlands, and coastal communities.
  • May be a potential fire risk.
  • Once established, it can survive fire, drought and frost.

Control Methods:

  • Integrated management essential.
  • Early detection increases the chances of control.
  • For long term control, vigorous improved pastures must be established to compete with serrated tussock to help prevent re-invasion.
  • Physical removal, e.g. grubbing with a mattock, is the most satisfactory method where this is practicable. Care must be taken to ensure seed is not spread during removal.
  • Glyphosate and flupropanate (Fenrock) herbicides are useful in some situations. For specific recommendations on herbicides for serrated tussock control, contact the Department of Primary Industry, Parks, Wildlife and Environment  Herbicides for Serrated Tussock Control
  • Visit DPIPWE’s website for more information on Serrated Tussock control
  •  N.B. The herbicides mentioned on this documents may not necessarily be registered for use on the plant referred to.

N.B. Always check the herbicide label before use.