Serrated Tussock

(Nassella trichotoma)
Serrated Tussock, image: Andrew Crane

Serrated tussock, © Andrew Crane

What is serrated tussock?

Serrated tussock is a perennial grass native to South America. It is a serious weed of pastures and native grasslands.
Serrated tussock is a declared weed under the Tasmanian Biosecurity Act 2019 and associated Regulations. The importation, sale and distribution of serrated tussock are prohibited in Tasmania.
Serrated tussock is also a Weed of National Significance (WONS).

How to identify serrated tussock

Serrated tussock is a perennial (long-lived) tussock-forming grass with a deep root system. The leaves of serrated tussock feel rough (or serrated) if the finger and thumb are drawn down the blade. Flower stalks usually appear in spring, but may appear earlier in dry years and later in wetter years. A tussock in full flower presents a distinctly purple appearance due to the large number of purple florets.
Serrated tussock is similar to several of Tasmania's native tussock grasses, and is frequently overlooked until it begins to flower, at which time it is easily recognisable. The following characteristics enable serrated tussock to be distinguished from native tussock grasses:

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).
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.
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).
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).
The seed head breaks off whole. The previous year's seed heads do not generally remain on the plant.
Flowering and seeding heads are a dark purple due to the colour of the two 'glumes' surrounding the seed (see illustration).
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).
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.

See the Nassella species identification comparison table below for more information on identification.

Serrated tussock infestation, © Andrew Crane

Serrated tussock in Tasmania

Large, established populations of serrated tussock are located in the south east of Tasmania, particularly around Rokeby, South Arm, Sandford and Richmond. Other populations are known on the east coast at Swansea and Little Swanport, King Island and more recently recorded infestations are in the southern and northern Midland grazing areas.
In Tasmania it is a significant weed of grazing land. The coarse leaves of serrated tussock are unpalatable, and dense infestations in pasture can completely smother all other desirable pasture species, 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.
A number of serrated tussock populations are found in the urban areas of Hobart. This may be a potential fire risk.

Legal status of serrated tussock in your area

The legal responsibilities of landholders and other stakeholders in dealing with serrated tussock are laid out in the Serrated Tussock Statutory Management Plan.
Use Table 1 (Zone A municipalities) and Table 2 (Zone B municipalities) in the Serrated Tussock Statutory Management Plan to find out whether your area falls in an eradication or containment zone.

Detailed management and control guidelines for serrated tussock can be found in the Serrated Tussock Control Guide. Refer also to Herbicides for Serrated Tussock Control. For further information see Weed Links and Resources.

See also

Serrated Tussock Control Guide

Spread of serrated tussock

Serrated tussock is spread by wind. As the seeds mature, the flower-head stalk becomes brittle, so that a strong wind can break off the whole head. The flower head is then blown along until it lodges against an obstacle where it releases the seeds.
The flower head is extremely light and can be blown considerable distances. A hectare of serrated tussock can produce over 2 tonnes of seed or about 500 million seeds.
Serrated tussock seed can also catch on the fleece of sheep, as well as be carried in mud on the hooves of livestock and implements, on vehicle tyres, and on firewood.
Seed may remain dormant for several years (anecdotal reports state 20 years, but it may be significantly shorter) so an area which appears to have been cleared of the weed may produce seedlings when the soil is later disturbed.

Integrated Management

For long term control, vigorous improved pastures must be established to compete with serrated tussock to help prevent re-invasion. Ploughing or spraying alone without pasture establishment is not effective because serrated tussock will regenerate from seed reserves in the soil (up to 1200 million seeds/hectare in old infested areas).
All control programs should aim at reducing the amount of serrated tussock available to germinate. When starting on a control program it is best to start on the prevailing upwind side of a serrated tussock infestation to try and limit the amount of seed blowing into control areas.
Serrated tussock seeds can only travel small distances on flat ground because they get caught up in fences and other grasses. But on hills, serrated tussock seeds are launched and will fly for many kilometres. These areas should be a priority for control works.
The principles and methods of serrated tussock control are:

a) Prevention
b) Chipping or spot spraying individual plants and small patches
c) Controlling large infestations
d) Replacing dead tussock with improved perennial pasture
e) Maintaining a competitive perennial pasture
f) Alternative measures
g) Continual follow up.

Prevention: avoid the introduction of serrrated tussock

Preventing the invasion of serrated tussock is the cheapest and most effective means of control.
Learn to identify serrated tussock, regularly check for it and act immediately to remove it.
Place stock which have grazed on serrated tussock in a holding paddock to allow evacuation of any faeces containing seed, before moving into a clean paddock.
Buy certified seed and avoid purchasing hay or stock from contaminated areas.
Establish tree belts or phalaris barriers along boundaries with infested properties to help reduce the amount of seed blowing into your property.
Keep pastures vigorous and manage grazing so that no bare patches develop.

Chipping or spot spraying

Spot spraying and chipping is used to control isolated or small patches of serrated tussock. This may be in a pasture situation, native grassland or urban environment.
Do not let serrated tussock establish beyond a scattered low density or control measures become expensive and difficult. This means that each year every paddock must be searched for serrated tussock.
For small infestations and isolated tussocks, chip tussocks with a mattock preferably before the tussocks set seed.
Do not chip out large patches of serrated tussock where a seed bank has built up: any soil disturbance will cause the germination of seeds.
The best time to remove serrated tussocks is when they are found. Be prepared! Keep a mattock in the back of the ute.
Herbicides registered for spot spraying serrated tussock are flupropanate and glyphosate. See Herbicides for Serrated Tussock Control for further information.
Spray to completely wet the plant and cause runoff. Add a dye to the spray mixture to identify areas sprayed.
Note that flupropanate is slow acting and can take 12 to 18 months to kill serrated tussock. Flupropanate will kill seeds that germinate soon after spraying. Always follow label instructions and note withholding periods when using herbicides.
Once serrated tussock has been removed, it is important to replace it with improved pasture; if the area is left bare, the weed will re-invade.

Controlling large infestations

Cultivation

On arable land suitable for cropping, serrated tussock can be controlled using a program of cultivation and repeated cropping, followed by pasture improvement.
Cultivation followed by cropping reduces the seed reserves available to germinate.
Serrated tussock seedlings cannot emerge when buried below 2 cm of soil. Chisel ploughing is not effective, but mouldboard ploughing and disc ploughing are successful in burying the seed.
Every effort should be made to cultivate and crop. Paddocks which cannot be cultivated have the disadvantage of not reducing the seed bank before sowing to pasture.
Burn in winter and plough soon after to a depth of 10 cm. Leave the paddock fallow and cultivate again in summer to remove any new tussocks. Crop for two years before sowing pasture to further reduce the reserve of serrated tussock seed in the soil.
Advice should be sought on the suitability of cultivation techniques on specific land to determine soil erosion risk.

Boom or aerial spraying

Serrated tussock can be boom or aerial sprayed. Flupropanate is registered for both applications and should be applied when there is adequate ground moisture to transport the chemical into the root zone where it is taken up by the plant.
See Herbicides for Serrated Tussock Control for further information. And always follow label instructions and note withholding periods.

Replacing dead tussock with improved pasture

After cultivation or spraying, an improved perennial pasture must be planted back to provide long term control of serrated tussock. Serrated tussock seedlings which germinate are weak and slow to establish and therefore can be out competed with vigorous grasses.
On non-arable land, pasture can be sown by air. Aerial pasture establishment is suited to stony barrier country and steep gorges.
Aerial pasture establishment is considered risky in areas receiving less than 550 mm of annual rainfall due to seed weathering and drying out.
Sow pasture seed in late autumn or early winter, one week after controlling annual weeds with a knockdown herbicide. Treat all pasture seed with an insecticide, to prevent ant harvesting. Treading seed into the soil using a large mob of sheep can improve seed-to-soil contact and reduce the risk of germinating seeds dying. Sowing into serrated tussock trash can also protect the seed and enhance establishment. Broadcast fertiliser either at sowing or soon afterwards.
If the land is arable but cropping uneconomical, then sow pasture and fertilise with a pasture drill. Serrated tussock may not have died at the time of sowing and the paddock will contain large amounts of trash. You will need to use a pasture drill with trash clearance. Sow one week after spraying in April to June.
Phalaris and cocksfoot are useful grass species to compete against serrated tussock. Phalaris is suited to heavy clay soils and is better able to compete with serrated tussock. However, cocksfoot can tolerate a lighter and less fertile soil than phalaris.
Also sow a mixture of subclover cultivars. Encourage the pasture to become dominant with clover in the first year which will smother out any new tussock seedlings and make nitrogen available to the improved grasses. The nitrogen will help the pasture to become grass dominant which will provide long term control of serrated tussock.
Avoid grazing new pasture until pasture grasses and clovers have set seed. This allows young plants to fully develop and produce seed which thickens up the pasture in the following year. Aerial sown pastures are slower to establish than those conventionally sown and need to be spelled into late summer. In late summer, graze down surplus pasture to promote autumn regrowth and clover germination. Spell the new pasture for a month after the autumn break to encourage clover germination.
Serrated tussock can germinate in response to rainfall in any season. It is critical to keep good pasture cover at all times to restrict the establishment of serrated tussock. In the second and third years of a new pasture, spell over spring and summer to smother out the many serrated tussock seedlings which will germinate.

Maintaining a competitive pasture

To maintain a vigorous perennial pasture, fertiliser will need to be applied annually in autumn.
Rabbits must be controlled before starting on a pasture improvement program.
Avoid overgrazing as this will encourage re-invasion of serrated tussock. Pasture should contain at least 80% ground cover at all times. If the pasture becomes invaded with weeds other than serrated tussock, herbicide manipulation could help to remove annual grasses or broadleaf weeds.

Alternative measures

Trees

Dense tree plantings which provide good shade can kill serrated tussock. Commercial pine plantations can be used to control serrated tussock.
Wind breaks also play a role in trapping serrated tussock seed and preventing them from blowing any further.

Burning

Annual burning can be used to control serrated tussock in areas of low rainfall and low soil fertility where improved pasture is not an option and the serrated tussock density is high.
Burning will not kill serrated tussock; however burning in winter will stop the majority of plants from setting seed and spreading.
Burning also reduces the fire hazard over the summer period.
Burning should only be used where serrated tussock is already at a high density. Burning serrated tussock which is not at a high density initially leaves bare areas where serrated tussock can further invade.
Consult your local Fire Authority before burning and seek NRE Tas advice on the suitability of this technique for your area.

Grazing

Goats will graze serrated tussock and can control the weed if the serrated tussock occupies less than 20% of the pasture.

Continual follow-up

Serrated tussock will re-invade an improved pasture, particularly if it is weakened or by the sheer amount of seed in the soil. However, re-invasion will be much smaller and slower than in an unimproved pasture.
Once tussocks re-invade an improved pasture they can be removed by spot spraying or chipping, aim not to let serrated tussock set seed. If the re-invasion is large then serrated tussock can be selectively removed from an improved pasture by using a blanket application of flupropanate. Applied in summer, when improved grasses are dormant or not actively growing, should not kill these pasture species, although some damage will occur. Phalaris is the most tolerant grass species to flupropanate.
Grazing down the improved pasture species before spraying at the correct rate will minimise pasture damage.
Once you start on a control program, make sure you complete it and do not give up! Serrated tussock can be controlled but you have to work at it.

More information

Herbicides for Serrated Tussock Control for detailed information herbicides for control of serrated tussock.
Or refer to the Weeds of National Significance - Serrated Tussock Weed Management Guide for further details on identification, control methods and developing a serrated tussock control program.
Serrated Tussock Property Control Plan - Lifecycle Calendar

Herbicides for Serrated Tussock Control

Nassella species identification comparison table

	Lobed Needle Grass	Cane Needle Grass	Texas Needle Grass	Chilean Needle Grass	Serrated Tussock
Status	Introduced Declared; an Alert List Weed	Introduced; Declared; an Alert List Weed.	Introduced; Declared; an Alert List Weed.	Introduced; Declared; Weed of National Significance.	Introduced; Declared; Weed of National Significance
Form	Tussock	Tussock	Tussock	Tussock	Tussock
Seed (outer casing of seed, the 'glume', removed to reveal detail.)
"Corona", the collar at seed base	Present	Present	Present	Present	Absent
'Awn", the bristle like seed tail	45-85mm double bent firmly fixed to seed coat	35-40mm Twisted and bent	35-60mm long Bent twice with 10-20mm to first bend	25-35mm Straight or double bent. Firmly fixed seed coat	10mm Straight Readily detached from seed coat
'Cleistogenes', or stem seeds	Absent	Present	Present	Present	Absent
'Ligule', the flap at leaf base
Overall dimensions	0.5-1.0m high 0.3 -0.5m across	to 1m high 0.3m across	1-1.5m high 0.2 -0.5m across	1-1.5m high 0.3 -0.6m across	1m high, 0.6m acros
* Images in table: © 2003 Weed Management Guides, Lobed needle grass, Chilean needle grass, Serrated tussock, C'wlth Dept of the Env't & Heritage. © Chilean Needle Grass & Serrated Tussock Ligule photos: Harry Rose (Wikimedia).

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