Nassella trichotoma

(Serrated Tussock)

from the Weeds of National Significance list

It looks like a native grass, in fact, if you didn’t know its story, you might think it would work well as an ornamental grass in a home garden and be tempted to collect and grow the seed (or dig up clumps). After all, it forms a large attractive tussock with thin, bright-green leaves and the long purplish flower and seed heads tend to weep to the ground. However, don’t be fooled. Nassella trichotoma (Serrated Tussock) is a significant weed with a lot of very bad attributes.

The plant can produce anywhere up to 140,000 seeds per year, which can stay viable in the soil for up to 13 years. The seed is also light, so it can be blown 20 kilometres away and more. It can also be transported on the muddy wheels of vehicles, in contaminated hay, and it will stick to animals and clothing. Individual plants are also long-lived, producing seed for about 20 years.

It invades pastureland and the bush, especially precious grasslands but it will also spread into forest. It can tolerate a high density, so it eventually eliminates most other plants. Stock find it unpalatable but if forced to eat it they will often starve to death because it is virtually indigestible. And that’s not all. Dense stands are a considerable fire hazard.

The individual plant pictured here has not developed the characteristic weeping (flopping) form that is a distinctive feature of the plant when the seed heads are mature (photo courtesy of Department of Primary Industries, Victorian Government). The second photograph, where it can be seen growing along a fence line, shows it in its distinctive summer form (photograph courtesy of the Victorian Serrated Tussock Working Group).

Getting rid of it poses a lot of problems. On the south coast of New South Wales, Serrated Tussock has been declared noxious in the W2 category, which means it must be suppressed and destroyed. In some areas it is so well established that this is not feasible.

Prevention is certainly the cheapest and most effective way of controlling this grass. For land owners, learning to identify the grass and acting immediately to remove it is the most important factor. Tree belts along boundaries with infested properties will help to reduce the amount of seed blowing in.

Spot spraying and physical removal (chipping out with a mattock) are suitable in areas with scattered infestation. Once the grass is established it’s difficult and expensive to remove. In pastures, the herbicides registered for serrated tussock control (spot, boom and aerial spraying) are flupropanate (Frenock11 Trademark of Crop Care) and 2,2-DPA. Currently flupropanate is unavailable in the market place and other chemicals are being evaluated for use. For further information contact DPI.

There is no selective herbicide for use in native grasslands. Spot spraying, weed wiping and manual removal are the only options.

Home gardeners should remain vigilant, as this grass has been found in nurseries from time to time. And don’t be tempted to collect seed from any wild grasses unless you can make a confident identification.

Serrated Tussock invades a variety of areas, from dry coastal through to river corridors, and it tolerates low nutrients and poor soil, fire, drought and frost.

The flowers are produced on an arching branched panicle that can be quite purple. The flowering branches expand with maturity. The seeds are about 1.5mm long and are enclosed in a pair of reddish-brown or purplish bracts. The heads droop and touch the ground when the seed is ripe.

The leaves are finely serrated (which can be felt), tightly rolled and about .5mm in diameter, with a white base.

Serrated Tussock is a close relative of Australian Austrostipa species and can be mistaken for Poa labillardiera mainly because it also forms a large tussock.

Sources:
CRC Weed Management (www.weeds.crc.org.au/main/wom_serrated_tussock.html )
Department of Primary Industries, Victorian Government
Department of the Environment & Heritage, Australian Government
Environmental Weeds, 2001, by Kate Blood, CRC Weed Management Systems, published by CH Jerram Science Publishers

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