Native Grasses Help Fight Weeds
October 4, 1999 The Southern Weekly Magazine
They may not look high tech, but native grass stands of speargrass (stipa sp.) and red-grass (bothriochloa sp.) on roadside reserves are potentially saving Coolamon Shire $190 per kilometre in herbicides for noxious weeds.
One of the major headaches for the Coolamon Shire according to weeds advisory officcr, James Smith. is horehound, with its ability to set enormous amounts of seed.
Last year, the cost of spraying 50km of horehound infested roadsides was $9500, or $l90 per kilometre.
And Mr Smith believes the Shire has only eradicated around 10 per cent of the infested sections.
"What we're observing is that if you can preserve the native grasses by using selective herbicides, they will out-compete any new weed seedlings," he said.
"If we go in with a broad spectrum herbicide, we get excellent weed control, but a bare area which is quickly filled with weeds. By using selective herbicides and preserving native perennial grasses to out-compete weed seedlings, there is virtually 100 per cent horehound seeding mortality.
"In areas with a good stand of perennial native grasses, the mop-up work amounted to half a day at a cost of around $200.
"While it is all well and good to establish a grass species which will out-compete the weeds, this comes at a cost.
"Added to the Costs of spreying for weeds, it just points out how valuable these existing native species are - don't overgraze them, don't cultivate and they will provide a major buffer against weed invasion."
Coolamon Shire, as part of the Eastern Riverina Spiny Burr Grass Action Program, is also looking at trialling the effect of native grasses such as redgrass, wallaby grass (danthonia .sp.) and kangaroo grass (themeda) on spiny burr grass.
Mr Smith hopes the grasses will be able to out-compete the noxious weed.
Wagga Wagga catchment manager with the Department of Land and Water Conservation, Rob Seriven said one of the reasons native grasses were competitive against weed invasion in areas which are not overgrazed is that many have an allopathic effect on other plants.
The grasses give out a toxin that restricts the growth of other plants, which explains the typical bare ground around native grass tussocks in undisturbed situations.