Cumbungi (Bullrush) Control

Alert!
Before you start clearing an infestation, make sure you are dealing with the introduced cumbungi. The broadleaf cumbungi and narrow leaf cumbungi are native species and should not normally be removed. These native cumbungi can provide shelter for waterbirds and other aquatic organisms, as well as being useful for reducing erosion of river banks.Cumbungi, Photo: T. Rudman

Do's and Don'ts of cumbungi control

Do's

  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see the Herbicides for cumbungi control link for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Revisit and regularly inspect the site and ensure follow-up is undertaken;
  • Consider a non-herbicide method first.

Don'ts

  • Don't start your control program without first planning your approach;
  • Don't allow an infestation to become established. Get in early!
  • Don't rely on just one treatment: follow-up is essential.

Spread of cumbungi

  • Cumbungi reproduces in two ways: long distance dispersal by seed, and the spread of dense infestations from rhizomes (underground stems).
  • Cumbungi seed may be transported by wind and water, in mud on the feet of birds and livestock, and on machinery.

Avoiding the establishment of cumbungi

  • Cumbungi quickly becomes a large and vigorous plant, so any new infestation should be treated as early as possible.
  • Destroying young plants, before they establish and produce seed, is the most effective method of control.
  • If an infestation becomes established, eradication in one season is difficult and follow-up work over two or three seasons will be required.

Physical removal

  • Small plants can be removed by hand-pulling or with a spade. Make sure all pieces of the roots and rhizomes are removed, otherwise the plant can quickly regrow.
  • Larger infestations can be removed by mechanical excavation. Care must be taken to avoid damage to the structure of the waterway.
  • Excavated material should be dumped well away from the water at a site where it can dry out and kill all plants.
  • Repeatedly cutting all leaves at 50-150 mm below the water surface can be used to control small infestations. First cut when the flowering period is well advanced (around January), with follow up cuts at 4 to 6 weekly intervals.
  • Most plants will die in the first year using this cutting method. A second year of treatment should finish off any plants which survive the first treatment.

Cultivation

  • If low water levels permit, an alternative to excavation may be to cultivate the site in autumn.
  • This brings root and rhizome material to the surface to dry out. This method gives good control over small infestations, and can reduce the size of large infestations to manageable levels.

Chemical control

  • A limited number of herbicides are registered for use on cumbungi in Tasmania due to problems with off-target effects on rivers. See Herbicides for Cumbungi Control for more information.
  • Using a herbicide has several disadvantages. The mass of decaying vegetation reduces a dam's holding capacity and can allow invasion by other weeds or a re-invasion of cumbungi.
  • Use of a backhoe, bulldozer or dragline may be needed to restore the dam to its original capacity.
  • Decomposition of the dead plant material can render the water unfit for use by stock.
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