Why it is a pest plant
|Production threat||Environmental threat||Public threat|
Australian sedge is a densely tufted, deep-rooted, perennial plant which can grow almost 1m tall. Unlike most sedges, which prefer swampy areas, Australian sedge grows in land which is seasonably dry. Larger infestations are eye-catching as they form a large dense colony. Australian sedge is distinguished in New Zealand by its distinctive flower/seed head.
- Flowering stems are triangular in cross section and sharply angled.
- Flowers are very small and grouped in catkin-like spikes, most of which are female.
- Flowers hang at the end of long thin nodding stalks.
- Seeds are small smooth triangular nuts.
- Seeds are enclosed within a long beaked covering about 5mm long.
- Leaves are about 5mm wide, Y-shaped in cross section (with gradually tapering tips), often exceeding the flowering stems in length.
- Leaf edges are harsh and will cut if you pull your fingers through the leaves.
- The sheath at the bottom of each leaf is dark brown.
Australian sedge forms dense tussock infestations 30-90cm high in pasture areas. It is unpalatable to stock and reduces farm production by crowding out pasture. In open grassland areas, Australian sedge is also a threat to native species as it competes with seedlings.
It establishes and spreads most rapidly on disturbed and exposed soil where pasture doesn’t thrive due to low soil fertility, drought, overgrazing or insect damage.
Australian sedge produces many seeds, which remain viable for three to five years. Once established, it can spread rapidly throughout the farm via livestock. The seed is quite heavy and most falls within 30cm of the plant. This creates an ever-increasing ‘mattress’ of Australian sedge.
Responsibility for control
All landowners/occupiers in the Waikato, on complaint from an adjoining neighbour, are responsible for controlling Australian sedge within 20m of their property boundaries and are required to work with Waikato Regional Council in areas where control programmes are in place. Australian sedge is also banned from being sold, propagated, distributed or included in commercial displays.
How to control australian sedge
Grubbing should only be used to deal with scattered isolated plants. It is a costly and ineffective method of control for large infestations. Breaking up the plant encourages seeds to germinate and the ground becomes reinfested. Australian sedge will regenerate from fragments, so all root stock must be collected and disposed of. It is necessary to recheck the site regularly for seedlings and regrowth.
Glyphosate is an effective herbicide against Australian sedge. The area should be checked and resprayed each year to kill new seedlings and regrowth. The optimum time for spraying is November through to March. The best protection against reinfestation from seed still in the soil is a dense pasture cover.
Safety when using herbicides
- Follow the instructions on the manufacturer’s label.
- Always wear protective clothing.
- Always minimise the risk to your other plants.
- Contact the supplier for further advice.
Summary of herbicides and application methods for control
|Herbicide rules will apply. You may need to notify neighbours if spraying. The Waikato Regional Plan explains the agrichemical (herbicides) use rule in section 6.2 in the Waikato Regional Plan.|
After initial control, it’s important to:
- clean out the site again at least annually to control regrowth
- stop weeds invading by replanting with non-pest plants (preferably native plants) once regrowth is no longer a problem.