Coolatai grass - it seemed like a good idea at the time

By David Walker
January 25, 2010

The scientists have classified it as Hyparrhenia hirta, but it is also known as ‘Tambookie Grass’ and ‘Common Thatching Grass’ in other parts of the world. In the North West of NSW, it has taken the name of the locality where it was intentionally introduced as a fodder plant and ground stabiliser in the 1940’s: the Coolatai area north of Warialda. 

It was not a smart move. Not only is the feed that it produces generally avoided by stock because of its low digestibility, but it is so aggressive that it has taken over large areas of the North West and is still spreading. 

Coolatai grass is a tall, tufted, summer active perennial, suited to a wide range of soil types. It is distinguished by paired seedheads (racemes) and grey-green leaves that are harsh to the touch. 

It is a particularly intractable problem in remnant areas of grassy woodland such as on travelling stock routes and reserves. It is spreading rapidly along roadsides and the operation of machinery such as slashers and graders used by local Councils and the RTA seem to be assisting its spread. The species appears to be able to displace native grasses even in situations where grazing by livestock is minimal. It affects the abundance of fauna, such as reptiles, frogs and ground-active invertebrates. 

It is difficult to control with herbicides, but some success has been achieved with glyphosate and fluproponate. The spraying of large areas is uneconomical.

Where Coolatai grass has infested grazing paddocks, the productivity of the land is seriously threatened. Under what we would consider to be good grazing management (i.e. the maintenance of groundcover at above 70% and the incorporation of ‘rest’ into the grazing system), it seems to thrive. Under such conditions, a huge bulk of useless ‘feed’ can be produced - highly combustible fuel that increases the risk of wild fires. 

Very high stocking pressures need to be maintained to keep it short and more palatable. In this situation paddocks are more at risk of erosion, and soil health will surely decline. However, under heavy grazing, the basal stems form a dense, hard mat, resistant to damage from grazing or fire. 

Thus the management that is needed to keep the Coolatai grass of at least some usefulness, also tends to give it further advantage over the plants that we want.

Clearly the best alternative is to prevent it becoming established in the first place. 

If you think that Coolatai grass may be establishing in your area, it would be highly advisable to work with neighbours and your DPI District Agronomist to devise a strategy to combat it. Once established, you will have to learn to live with it. You won’t beat it.

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