Serrated Tussock Nassella trichotoma (Nees) Hackel ex Arechav.
Synonyms - Stipa trichotoma
Family: - Poaceae.
Names:
Nassella is from the Latin nasus meaning nose, which refers to the nose like shape of the flattened flower stalks of some species in this genus.
Trichotoma is from the Greek thrix meaning hair and tome meaning cut and refers to the fine sharp leaves.
Serrated Tussock refers to the serrated leaves and the tussocky growth habit.
Other names:
Nassella Tussock (NZ)
Yass River Tussock.
Summary:
Serrated tussock is a perennial, drought resistant, tussock-forming grass, up to 500 mm high by 750 mm diameter and 250 mm diameter at the base, with a deep, fibrous root system and fine seed heads and seeds that are readily dispersed by wind. It is purple when flowering and straw coloured after the seeds ripen.
Description:
Cotyledons:
One
First leaves:
Young plants are erect and densely tufted with tightly inwardly rolled leaves.
Leaves:
Many, emerge from the base of the plant forming a large compact tussock.
As the plant grows to maturity, the later leaves are longer, the tips turning a 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. This characteristic is not, however, restricted to Serrated Tussock and is not diagnostic for the species. By the time the tussock is at the flowering stage the leaves are long and drooping. The tussock is made up of small groups of leaves that may be easily separated.
Blade - Bright green during summer to yellow green in winter. The tips of old leaves bleach to a fawn colour. The base of the leaf is white. The leaves are fine, 200-500 mm long, finely bristled, rough to touch or smooth, white base, tightly rolled to give a cylindrical appearance.
Ligule - Membranous, white, 1 mm long, rounded and hairless.
Sheath - Very short. Whitish and more slender and closely packed than in the native tussocks
Stems:
Densely tussocky, up to 500 mm high ( about twice as long as the leaves), slender, initially erect and droop with age, many branched, and usually break off at the base after seeds mature. Flowering stems begin to appear in spring or earlier in dry years and later in years when an adequate water supply allows a longer period of vegetative growth.
Flower head:
Panicle, up to 350 mm long, carried on slender stems slightly longer than the leaves. The flower head is an open, lax, branched panicle with the primary branches in pairs, secondary branches in pairs or 3's, each pair distant from the next. The branches are slender, brittle, thread like and drooping. The flowers are small and inconspicuous near the ends of branchlets. When ripe the heads droop over to touch the ground. There is a single seed at the end of each branch. The seed head is fine purple and slightly taller than the leaves. When ripe the whole seed head breaks off and can be blown in the wind.
Flowers:
A tussock in full flower presents a distinctly purple appearance due to the large number of purple florets.
Spikelets - On thread like stalks.
Florets - purple in colour initially then turning pale straw-coloured, about 2 mm long, with a tuft of short hairs at the base and a long slender twisted awn from the tip, produces one seed.
Glumes - Egg shaped to broadly lance shaped, curving around the plump lemma, 3 nerved, slender tapering tip, purplish near the base and membranous near the tip. Lower glume 6 mm long. Upper glume slightly shorter.
Hardened extension of the flowering glume (callus) is short, obtuse tipped, with a 30 mm, thread like, slightly bent and scarcely twisted awn arising from the flat top of the callus.
Palea -
Lemma - Shortly egg shaped, rough to touch, 1-2 mm long.
Stamens -
Anthers -
Fruit:
Seed is enclosed in purple to red-brown bracts.
Seeds:
Up to 100,000 per plant, 1.5-2 mm long, white silky hairs at the base, twisted, 20-30 mm awn that has tiny barbs near the top.
Roots:
Densely fibrous, shallow, mainly in the top 200 mm of soil with some deeper roots.
Key Characters:
It is often difficult to distinguish from native tussocks. Check for the following;
Small, white, hairless ligule. Serrated leaf the may only be apparent when the leaf is drawn from tip to base through the fingers. Leaf rolls easily between the finger and thumb. Leaf is white at the base. Seed stalks break off at the base and don't remain on the parent tussock. Distinctive purple appearance during flowering that changes to a golden colour once the seeds ripen.
Biology:
Life cycle:
Perennial. Seeds germinate at any time of the year with a flush in autumn and winter. Seedlings establish roots quickly and are difficult to pull from the soil at a young age. In the first year they form a tuft of tightly packed leaves. Flowering generally occurs for the first time when the plant is about 18 months old but in poorer situations it may take 4 years until flowering. Individual plants increase in size by tiller production, and a mature tussock may measure 300 mm across the base with the drooping leaves covering a diameter of almost 1000 mm. Flower stems emerge from the base in spring and seeds form during summer. When the seeds are ripe the stalk becomes very brittle, the first strong winds 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. Autumn and winter frost bleach the leaves. Old flowering stems die as do many leaves. These are replaced each year. The tussock survives for many years.
Physiology:
Drought tolerant.
High fibre content of 55-86%, similar the wheat straw.
Low protein content of 4-6%.
Quality and digestibility is too low to maintain stock body weight. Sheep grazing Serrated Tussock lost 190 g body weight/day in trials in NSW. Contrastingly, in Argentina it is regarded as useful fodder and is often depleted by over grazing.
Reproduction:
By seed.
Flowering times:
Spring to summer.
November to January in Victoria.
Seed Biology and Germination:
Produces large numbers of seeds. Up to 2 tonnes/ha of seed may be produced.
Produces dormant seed that may remain viable in the soil for 15 years or more.
Seed passes through the gut of cattle and sheep without losing viability. It takes at least 4-6 days before all seed is passed from the gut of sheep and cattle.
Vegetative Propagules:
None.
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Serrated Tussock is capable of rapid spread. The primary natural method of dispersal is wind. Seeding heads are extremely light and can be carried by the wind over several kilometres. In Tasmania it is obvious that man's activities have been responsible for introducing and spreading the weed. The tuft of basal hair and the awn of the seed cause it to catch on wool, fur, bags and clothing. It may be picked up in mud on the hooves of livestock or on cultivating implements, in vehicle tyres or on firewood. It is also spread in hay, crop and pasture seed and animal droppings.
It has been estimated that a hectare of dense tussock can produce over a 2 tonnes of seed or about 500 million seeds.
Quarantine measures are preventing its spread in Tasmania.
Origin and History:
Argentina, Chile, Peru and Uruguay and South American pampas grasslands.
First recorded in New Zealand in 1905 and now is one its worst weeds.
Introduced to Australia around 1900 but not recorded until 1935 at Yass in NSW.
First recorded in Victoria in 1954.
First recorded in Tasmania in 1956 from pea seed introduced from NZ 30 years earlier.
Distribution:
ACT, NSW, TAS, VIC.
In Tasmania the known infestations are restricted to parts of the Clarence, Sorell and Tasman municipalities and a small area in the south of King Island.
Habitats:
Climate:
Sub humid, subtropical and warm temperate.
In many rainfall zones.
Soil:
On many soil types.
Plant Associations:
In many plant communities.
Significance:
Worst weed of NSW, infesting 700,000 ha and costing $12.5M/year in lost production. A large control program from 1979-86 reduced the area to 500,000 ha.
100,000 ha is infested in Victoria with a potential to infest 4.2 million hectares.
It is a significant weed of NZ, South Africa and North America.
Beneficial:
Detrimental:
Serious weed of pasture.
Unpalatable to stock and of little nutritive value.
Weed of pasture, lightly timbered areas, open grazing country, roadsides and waste places.
Reduces carrying capacity to 0.5 dse/ha and is claimed to be the single plant that can cause the greatest reductions in carrying capacity in Australia.
Seed contaminates wool.
Sharp bristles on the seed may damage the mouths of stock.
Toxicity:
May cause fibre balls in the gut of animals causing loss of condition and death.
Sharp awns on the seed damage the mouths of sheep and the rough foliage wears the teeth.
Legislation:
Noxious of ACT, NSW, VIC, SA, TAS.
Prohibited weed.
Management and Control:
Implement farm hygiene strategies.
Purchase stock from Serrated Tussock free areas. Use clean seed and clean machinery.
Plant shelter belts to reduce spread by wind from infested properties.
Remove odd plants by chipping in autumn to spring before seed is produced.
Spot spray plants in spring to early summer.
Fertilise and spread pasture seeds on treated areas.
Burn or slash top growth in winter, mouldboard or disc plough to 10 cm to turn tussocks over, the cultivate to control seedling in preparation for replanting to pasture (preferably perennial) in the following autumn/winter.
Use Flupropanate, 2,2-DPA and tetrapion or flupropanate for chemical control.
Thresholds:
In New South Wales and New Zealand dense infestations have made large areas of improved and partially improved pasture completely unproductive.
Eradication strategies:
Seed dormancy makes eradication of established infestations a long-term operation.
Shear sheep coming from infested areas. Allow a week on clean pastures to void seed from the gut.
Manually remove isolated plants ensuring all the basal tussock is removed. Spraying is often more effective. Burn the area. Plough infested areas in spring and repeat as necessary through summer. Plant competitive pasture species and don't graze in the first season, Phalaris is often used. Control rabbits. Aerial application of seed, fertiliser and herbicides is used in difficult terrain.
Flupropanate or mixtures with 2,2 DPA is now used in preference to TCA and 2,2 DPA in many situations. Glyphosate is also effective and widely used.
Planting pines may also control it. Seeding of Serrated Tussock is usually eliminated within 6 years of planting and most old tussocks have died within 10 years of planting.
Grazing light infestations with goats helps reduce its spread and establishment.
Even small plants are very difficult to pull by hand.
Herbicide resistance:
Biological Control:
In South America some fungi and bacteria attack the weed.
Related plants:
None.
Plants of similar appearance:
It is similar in general appearance to several Tasmanian native tussocks (Poa spp.) but the seed head clearly distinguishes Serrated Tussock from the native tussocks.
Silver Tussock (Poa labillardieri) and most other native grasses have a very small ligule that is fringed with tiny hairs.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P49. Diagram. Photo.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P54-55. Diagram.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P17. Diagrams.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #864.1.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P111-115. Photos
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.