 INTRODUCTION
Giant Parramatta grass (Sporobolus fertilis formerly Sporobolus indicus var major) is a serious, aggressive weed that has invaded large areas of pasture on the North Coast of NSW. This introduced pest is a declared noxious weed and continues to spread along the coast and inland with extensive infestations on the Far North Coast, Manning and Hunter River regions and isolated infestations on the South Coast, Northern Tablelands and Slopes areas of NSW and South-East Queensland.
Giant Parramatta grass is a threat to grazing lands because:
• it can reduce pasture production, animal performance and the value of grazing land;
• it is a vigorous, persistent and invasive perennial grass of poor quality and low palatability;
• it is well adapted to a wide range of climatic and pasture conditions and is capable of rapid spread on the North Coast of NSW, southern Queensland, and inland summer rainfall areas;
• it produces a large number of seeds that can remain viable in soil for several years;
• seed is spread by vehicles, machinery, livestock and floods (it is not spread by the wind).
Giant Parramatta grass is also a problem along roadsides and in national parks, forests, picnic areas, parks and ovals. These infestations are a source of seed which can spread to clean areas, as well as being a fire hazard in winter and spring.
IDENTIFICATION
Giant Parramatta grass is a coarse tussocky grass that grows to a height of 70 cm to 2 m. The seed heads are up to 40 cm long and resemble a rat’s tail (see figure 1). The branches at the bottom of the seed head often droop away from the central stem. The seeds, which are about the size of sugar grains, form at the ends of each floret. They are initially white and turn yellow-brown at maturity.
Giant Parramatta grass flowers and seeds in the frost-free period of the year, with the main seeding in late summer/autumn. Single tussocks grow up to 40 cm in diameter and produce more than 200 seed heads per year. The tussocks hay off in the autumn, leaving a distinctive straw of seedless heads.
Giant Parramatta grass is often confused with two similar grasses:
• A smaller species of Parramatta grass (Sporobolus africanus, formerly Sporobolus
indicus var capensis) is similar to the giant species, except in size and aggressiveness. This smaller species (usually up to 50 cm high) is very common but is not a serious weed. • Giant Rats Tail grass (Sporobolus pyramidalis
and S. natalensis) introductions from Africa that are serious weeds in Queensland and isolated areas of the NSW Far North Coast.
These species have a growth habit and appearance very similar to giant Parramatta
grass, except that at maturity they have much more open seed heads and are often slightly taller and coarser with longer leaves. These aggressive weeds should also be controlled in the same way as giant Parramatta grass.
Light infestations
• Cut seed heads and put them in a bag for destruction before digging out or spraying the plant. Dig out or spot spray any giant Parramatta grass as soon as you find it. (For more information on spraying consult the table on page 11. After digging out plants it is good to fill the divot with Kikuyu runners or
seed of grasses that will compete with giant Parramatta grass seedlings.
• Don’t overdo your spot spraying — only direct the herbicide onto the crown and green leaves. Spraying the seed heads is ineffective, and only spreads the herbicide further, often killing surrounding desirable species.
Heavier infestations If the infestation is too heavy to be spot sprayed
or dug out, you need to decide whether to:
• keep the existing pasture base and manage the giant Parramatta grass to reduce its population and minimise its effects, or • remove the existing pasture and replace it with more competitive and productive species.
Managing giant Parramatta grass in a pasture If you decide that removal is not economical or is physically impossible, then your emphasis should be on containment, and getting the best out of the pasture. How you do this depends on
the type of country and other pasture species present.
For low fertility country, the main improved pasture option to reduce the impact of giant Parramatta grass is to undertake a minimal cost pasture program involving the following steps.
• Graze hard and/or wick wipe in autumn. Slashing or mulching to reduce heavy autumn growth may also be an option but remember that slashing can spread seed and is expensive (see the note below on slashing).
• Consult a local pasture sowing guide or adviser and surface sow or direct drill well adapted pasture legumes (e.g. Haifa white clover, Wynn cassia, Maku Lotus) with appropriate fertiliser.
• Follow up with appropriate fertiliser topdressing to promote good legume growth.
• Use a glyphosate wick wiping program to progressively remove the giant Parramatta grass (see the section on wick wiping (page 6) for details.
• As the pasture develops, the option of using flupropanate at a later stage may also be feasible but not for pasture used by lactating dairy stock.
Another option is a ‘live with it’ method, where economics do not justify other control options.
If grazed short and kept leafy, giant Parramatta grass has similar quality to carpet grass in summer and is better quality than carpet grass in spring.
However, when it gets rank and in seed its feed quality is very poor.
Therefore grazing management should aim to keep giant Parramatta grass as short as possible through higher intensity stocking, wick wiping or judicious slashing. ‘Chemical slashing’ using sub-lethal rates of glyphosate through wick
wipers is a cheaper alternative to slashing.
Subdividing large paddocks with regular rotation of stock helps to increase grazing intensity.
A note on slashing
Slashing when the plant is in seed can rapidly spread the seed. Slashing when seeding is only recommended where giant Parramatta grass is dominant, as slashing sparse infestations when seeding can rapidly increase the density of the
infestation.
If the ‘live with it’ approach is used then it is vital that seed be prevented from spreading from infested properties to clean ones. Keeping roadways, tracks, yards and fence lines adjoining clean neighbours free of giant Parramatta grass
assists in reducing the spread of seed.
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